Measurement technique
The best arm to check blood pressure is whichever one reads higher, and the only way to find out which one that is on your body is to measure both. Do it once, properly, on an ordinary day when nothing unusual is going on. From then on, use that higher arm every single time so your readings are comparable from week to week. Most people never run this test, pick an arm out of habit, and quietly under-measure themselves by 5 to 10 mmHg for years. If you want to see how much a simple arm swap changes the pressure your organs actually experience, put both sets of numbers into the mean arterial pressure calculator and look at the gap.
There is a second reason the both-arms test matters, and it has nothing to do with picking a favorite cuff position. A consistent difference between your arms of more than about 10 mmHg systolic is itself a finding. It has been linked in large pooled analyses to a higher risk of cardiovascular events, and a very large gap can point to a narrowed artery under the collarbone. So the test costs you four minutes and can hand your doctor something genuinely useful.
The short answer: both arms once, one arm forever
Here is the rule in full, because the popular version of it is wrong. On your first serious measuring session, take a reading in your right arm, then a reading in your left arm, then a second reading in each, alternating. Average the pair for each side. Whichever arm produced the higher systolic number becomes your measuring arm from that day on. Write it on a sticky note and put it on the monitor case, because six months from now you will not remember.
The reason for choosing the higher arm is not pessimism. It is that the higher arm is the one closer to the true central pressure. A lower reading in one arm usually means something is damping the signal on the way down that limb, which makes that arm a bad proxy for what the heart is pushing against. Guidelines from the American Heart Association and from European bodies agree on this point even where they disagree about thresholds, which they often do. If you want the threshold argument laid out properly, the piece on what counts as a normal blood pressure range covers where the US and European numbers part company.
Does it matter what arm you take blood pressure on? For most healthy adults the honest answer is that the difference is small, often 2 to 5 mmHg, and small enough that it will not move you between categories. But you cannot know you are one of those people until you check. Roughly one adult in ten has a between-arm gap of 10 mmHg or more, and those are exactly the people for whom arm choice quietly decides whether they get treated or not. A reading of 138 on the low arm and 148 on the high arm is the difference between a conversation about lifestyle and a conversation about medication.
There is a related habit worth building at the same time. Arm choice only pays off if everything else about the reading stays constant, which is why the companion guide on how to get a good blood pressure reading is worth reading alongside this one. Same arm, same chair, same time of day, same cuff. Change one thing and you have changed the experiment.
The one-line version: measure both arms at your first session, use the arm with the higher average for every reading after that, and mention any gap above 10 mmHg systolic to your doctor.
Quick reference: arm, body position and what to do
This table is the whole article compressed. Each row is a situation people actually search for, with the practical instruction rather than the textbook hedge. The detail behind every row follows further down.
| Situation | What to do | Why it matters |
|---|---|---|
| First time using a home monitor | Measure both arms, twice each, alternating sides | Establishes your measuring arm and reveals any between-arm gap |
| Every reading after that | Use the arm with the higher average, always the same one | Consistency is what makes a week of readings comparable |
| Both arms read within 5 mmHg | Pick either arm, then stick with it | A gap that small is inside normal measurement noise |
| Gap of 10 to 15 mmHg systolic, repeatable | Use the higher arm and tell your doctor at the next visit | Linked to raised cardiovascular risk in pooled patient data |
| Gap above 20 mmHg systolic, repeatable | Ask for it to be checked properly, not urgently but not ignored | Can point to narrowing in the subclavian artery |
| Mastectomy, lymph node removal, dialysis fistula on one side | Use the other arm, no exceptions for the fistula | Cuff inflation can damage the access site |
| Recent pacemaker on the left | Use the right arm while the site heals, then either | Comfort and wound protection, not device interference |
| Arm resting in your lap | Move it to a table at mid-chest height | A lap position has been shown to add roughly 4 mmHg systolic |
| Arm hanging at your side | Support it, always | Unsupported has been shown to add roughly 7 mmHg systolic |
| Legs crossed at the knee | Uncross, feet flat on the floor | Crossing has been shown to add several mmHg systolic |
| Lying down | Fine, but keep the arm at heart level and label the reading | Supine numbers are not interchangeable with seated ones |
| Standing | Only as a deliberate orthostatic check, not as your routine reading | Standing pressure moves for the first three minutes |
| Ankle or leg reading at home | Do not use it as a substitute for an arm reading | Legs read higher normally, and the useful version is a clinical ratio test done in an office |
Notice how many of these rows are about position rather than side. That ratio is honest. For the average reader, fixing posture will change the number more than switching arms will, which is why the posture sections below are longer than the arm sections. Arm choice is a one-off decision. Posture is a mistake you can repeat every single morning.
Why are blood pressures different in each arm?
Blood leaves the heart through the aorta and then splits. On the right side of your body, the branch that eventually feeds your arm comes off a short shared trunk that also supplies the right side of your head. On the left, the artery to your arm usually branches off the aortic arch directly, a little further along. Different path, different angle, slightly different pressure wave by the time it reaches the cuff. That plumbing asymmetry is the standard explanation for why the right arm reads a touch higher than the left in most people, and the effect is genuinely small, usually a few mmHg.
The plumbing story is not the whole story though, and anyone who tells you it is has stopped reading at the first paragraph. Four other things move the number, and in real people they usually matter more.
Arterial narrowing
Plaque in the subclavian artery, the one running under your collarbone, throttles flow to that arm and drops its reading. This is the reason a large one-sided gap gets taken seriously. It is the same disease process described in the article on what drives high blood pressure in the first place, just concentrated inside one vessel.
Muscle bulk and arm shape
A heavily muscled or conical upper arm changes how cuff pressure transmits to the artery underneath. Handedness alone can leave one arm measurably thicker. That is a cuff fit problem more than a circulation problem, and the guide to sizing a blood pressure cuff explains how much a mismatch can distort things.
Order of measurement
The first reading of any session tends to run high because you are still settling. Measure right then left and you have handed the right arm an unfair advantage. Alternating sides and averaging cancels most of this out.
Old injury or surgery
A fractured collarbone, a repaired shoulder, thoracic outlet compression, or scar tissue from node removal can all reduce flow down one limb without causing any symptoms you would notice.
So why is my blood pressure higher on my right arm? Usually because that is simply your baseline anatomy, and if the gap is under 10 mmHg there is nothing to investigate. Why is one arm blood pressure higher by a lot? That is a different question, and it deserves a real answer from a doctor rather than a search result. The distinction between a normal small gap and a meaningful one is the single most useful thing on this page, and the next two sections are built around it.
One more source of confusion deserves naming. People compare arms on different days, with different cuffs, after different breakfasts, and then conclude their arms disagree. They do not. The readings disagree, which is not the same thing. Blood pressure moves constantly, and even the same arm measured twice five minutes apart will differ. Anyone who has watched their own numbers jump will recognize the pattern described in the piece on what causes a blood pressure spike. A valid arm comparison happens inside a single sitting, minutes apart, or it is not a comparison at all.
How to compare your two arms properly
This takes about ten minutes including the rest period. Do it once, then never again unless something changes. Use the same monitor for both arms, because comparing an upper-arm cuff against a wrist device tells you nothing except that they are different devices. If you are still choosing hardware, the rundown of the most reliable blood pressure monitors will save you buying twice.
Sit still for five minutes first
Back against the chair, feet flat, legs uncrossed, nothing to read, no phone. No coffee, cigarette or exercise in the previous half hour. Empty your bladder before you start, because a full one adds several mmHg and will do it unevenly across a ten minute session.
Take the first reading on the right arm
Bare arm, cuff on skin, the artery marker over the inside of the elbow, two fingers of space above the crease. Rest the arm on a table so the middle of the cuff sits level with the middle of your chest. Say nothing while it inflates.
Wait one to two minutes, then measure the left arm
Move the cuff over rather than using a second cuff. The pause matters because the first cuff inflation leaves the limb briefly congested and the next reading on that same arm would be affected.
Repeat the pair in the same order
Right again, pause, left again. You now have two readings per arm. If the two readings on one arm differ by more than about 10 mmHg systolic from each other, you were not settled. Rest longer and redo the set.
Average each side and subtract
Take the mean systolic for the right, the mean systolic for the left, and find the difference. Do the same for diastolic, although the systolic gap is the one that carries the clinical meaning.
Confirm anything large on a second day
A single session showing a 16 mmHg gap is a hypothesis, not a finding. Repeat the whole protocol on a different day before you treat it as real, because one-off gaps are common and mostly meaningless.
Clinics sometimes use two synchronized monitors and measure both arms at exactly the same moment, which removes the order problem completely. You cannot easily do that at home, and the alternating method gets close enough. The technique of measuring both sides at once is one of the few places where a manual setup has an advantage, and the walkthrough on how to check manual blood pressure explains why a trained ear with a stethoscope still beats some automatic devices on awkward arms.
Between-arm difference = higher arm systolic minus lower arm systolic
Example: right 146, left 132, difference = 14 mmHg
Use the right arm from now on, and mention the 14 mmHg gapHere is a worked example with the full arithmetic, because the abstract version never quite lands. Say your right arm gives 144/88 then 142/86, and your left gives 133/84 then 131/82. Right averages 143/87, left averages 132/83. The systolic gap is 11 mmHg. Your measuring arm is the right one. Now run the mean arterial pressure for both. Right: 87 + (143-87) / 3, which is 87 + 18.7, about 106 mmHg. Left: 83 + (132-83) / 3, which is 83 + 16.3, about 99 mmHg. Seven mmHg of difference in perfusion pressure depending purely on which sleeve you rolled up. The MAP calculator will do that arithmetic for you if you would rather not.
That example also shows why the higher arm is the safer default. At 143/87 you are firmly in stage 2 by US categories. At 132/83 you are in stage 1. Same person, same minute, two different conversations with a doctor. If you want to see how those cutoffs are drawn and why the American thresholds sit lower than the European ones, the explainer on whether 130/80 counts as high lays out the boundary case.
Should blood pressure be the same in both arms? What the gap means
No, and expecting identical numbers is the mistake. Should blood pressure be the same on both arms in a perfectly healthy person? Roughly, yes, within a handful of mmHg. In practice, measurement noise alone guarantees a small difference every time. The question is where small stops and meaningful starts, and guidelines have been arguing about that line for a decade.
| Systolic gap between arms | How to read it | What to do |
|---|---|---|
| 0 to 5 mmHg | Normal. Indistinguishable from measurement noise | Pick the higher arm anyway and move on |
| 6 to 9 mmHg | Common and usually unremarkable | Use the higher arm consistently, no action needed |
| 10 to 14 mmHg, repeatable | The threshold most current guidance now flags | Mention it at your next appointment |
| 15 to 19 mmHg, repeatable | The older, more conservative threshold. Taken seriously by every guideline | Ask your doctor to confirm it and consider vascular assessment |
| 20 mmHg or more, repeatable | Suggests significant narrowing on the low side | Get it evaluated. Not an emergency, but not something to file away |
| Large gap that appears suddenly with chest or back pain | Different situation entirely | Emergency care. A sudden gap with tearing chest pain is a red flag |
The evidence here is better than most people assume. Pooled analyses of individual patient data across many cohorts have found that a wider between-arm systolic difference tracks with higher rates of heart attack, stroke and death over the following years, and that the relationship appears to be continuous rather than switching on at a magic number. That is why the flagging threshold drifted down from 15 to around 10 in recent guidance. It is also why nobody should panic at 11 mmHg. A continuous risk relationship means an 11 mmHg gap carries slightly more risk than a 4 mmHg gap, not that it belongs to a different disease category.
What a large gap actually signals, most of the time, is atherosclerosis somewhere in the arterial tree. The arm difference is a window, not the problem itself. Somebody with a 22 mmHg gap and a cholesterol problem and a smoking history is being told something about their whole vascular system, which is the same message delivered by the article on why high blood pressure develops and the one on what smoking really does to blood pressure. The gap is useful because it is easy to find with equipment you already own.
Two caveats keep this honest. First, a large measured gap is often just bad technique, which is why the repeat-on-another-day rule exists. Second, in a small number of people the low arm is low because of a congenital variation in their arteries that has been there since birth and means nothing. Your doctor can usually sort that out by feeling pulses in both wrists, which takes about fifteen seconds.
Compare the perfusion, not just the top number
Two arms can differ by 12 mmHg systolic and only 3 mmHg diastolic, which changes mean arterial pressure less than you would expect. The mean arterial pressure calculator shows you the pressure your kidneys and brain actually see, and the background piece on how to find mean blood pressure explains why that figure often matters more than systolic alone.
Do you take blood pressure on the left or right arm day to day?
Once the comparison is done, the answer stops being a general question and becomes a personal one. Your arm is whichever arm won. Not the left because a nurse used it once. Not the right because you are right-handed. Whichever one read higher on the day you tested properly.
The reason the left arm has a reputation is practical rather than physiological. In a clinic, the patient sits with the left side toward the examiner and the equipment, so the left arm is simply easier to reach. That convention leaked into public understanding as a rule, and it is not one. Can you take blood pressure on the right arm? Yes, completely. What arm should you take your blood pressure on if you never did the comparison? Use the right, because it reads slightly higher in most people and slightly higher is the safer error to make.
Handedness gets raised constantly and it is mostly a red herring. Your dominant arm may be a little more muscular, which can affect cuff fit, but there is no meaningful pressure difference caused by which hand you write with. If your dominant arm is noticeably thicker, the fix is a larger cuff, not a different arm.
One genuine practical point favors the non-dominant arm. Home readings should be taken while you sit still and do nothing, and it is easier to keep your dominant hand free for pressing the button and writing the number down. If both arms read within a few mmHg of each other, using the non-dominant one is a fair tie-breaker. If they do not, the higher arm wins regardless of convenience. The routine described in the guide to the best time of day to check blood pressure assumes you have already settled the arm question and are keeping it fixed.
Which arm to take blood pressure with a pacemaker
An automatic cuff does not interfere with a pacemaker. There is no electrical interaction. The reason people are told to use the opposite arm after implantation is wound healing and comfort. A device sits under the skin below the collarbone, usually on the left, and repeated cuff inflation over a fresh surgical site is unpleasant and can disturb healing. Once the site has healed, which typically takes several weeks, most people can use either arm again.
The one thing to check is whether you also have leads, lines or a monitoring device that your cardiology team wants left alone. Ask them directly at your follow-up. It takes one question and removes the guesswork permanently. This is also the moment to ask whether they want your readings taken at a particular time relative to your medication, a question the article on the best time to take blood pressure medication covers in more depth.
Arms you should not use, and how firm each rule really is
Some of these rules are absolute and some are inherited caution. Being clear about which is which helps you follow the ones that matter instead of treating them all as folklore.
Dialysis fistula or graft. Absolute. Never inflate a cuff over an arm with a functioning arteriovenous access. The pressure can clot or damage it, and losing a fistula is a serious event for someone on dialysis. This one has no exceptions and no debate, and it applies to the whole arm, not just the site itself.
Arm with an IV line, PICC or infusion running. Absolute in practice. Cuff inflation interrupts the infusion and can force blood back up the line. Use the other side.
Fresh injury, fracture, burn or open wound. Obvious but worth stating. A cuff squeezing to 180 mmHg over a healing fracture is genuinely painful and the pain response will corrupt the reading anyway, in the way described in the piece on whether pain raises blood pressure.
Side of a mastectomy or axillary lymph node removal. Standard advice, weaker evidence than most people realize. The concern is triggering or worsening lymphedema. Recent studies have struggled to demonstrate that blood pressure cuffs actually cause it, and some cancer centers have relaxed the rule. Even so, if you have a usable arm on the other side, use it. There is nothing to gain by testing the question on yourself.
Arm weakened by a stroke. Not forbidden, but readings from a limb with reduced muscle tone and altered circulation are less reliable. Use the unaffected side where possible and say so in your log.
Recent pacemaker or defibrillator site. Temporary. Avoid while healing, then return to normal. No device interference is involved.
If both arms are unavailable, which does happen, that is when leg or ankle measurement enters the picture as a genuine clinical technique rather than a home shortcut. That is covered further down, along with why the numbers are not interchangeable.
A last note on rules people invent. Nothing about a tattoo, a recent flu shot, a blood donation from yesterday or an old sprain rules an arm out. The list above is the list. Everything else is worth using if it gives you a reliable reading, and reliability is mostly about cuff fit and stillness rather than history. If you are unsure whether an odd reading came from the arm or from the day itself, repeat it properly on the same arm before you believe it.
Posture: the part that costs more than arm choice
Pick the wrong arm and you might be off by 5 mmHg. Sit badly and you can be off by 15. That ratio is not intuitive, and it is the reason clinics spend more time on chairs than on sides. Here is what each posture error is worth, based on published measurement studies rather than guesswork.
| Posture error | Typical effect on systolic | Correct version |
|---|---|---|
| Back unsupported, sitting on a stool or the edge of a bed | Adds several mmHg, more to diastolic than systolic | Chair with a back, spine against it |
| Feet dangling or resting on a rung | Adds a few mmHg | Both feet flat on the floor |
| Legs crossed at the knee | Adds roughly 3 to 8 mmHg | Uncrossed, thighs parallel |
| Arm resting in your lap | Adds roughly 4 mmHg | Arm on a table, cuff at heart level |
| Arm hanging unsupported at your side | Adds roughly 7 mmHg | Arm on a table, cuff at heart level |
| Talking during the reading | Adds up to 10 mmHg | Silence, including not answering the phone |
| Full bladder | Adds up to 10 mmHg | Use the bathroom first |
| Cuff over a shirt sleeve | Unpredictable, sometimes large in either direction | Bare skin |
| No rest period before measuring | Highly variable, often 10 mmHg or more | Five quiet minutes, seated |
Stack three of those and you have manufactured a hypertension diagnosis out of furniture. Someone who sits on a kitchen stool with crossed legs, holds the cuffed arm in their lap and chats while the machine runs can easily read 20 mmHg above their true seated pressure. They then repeat the ritual daily and conclude their pressure is climbing. It is not. Their chair is.
The largest single trial on arm position was a crossover study that put the same people through desk-supported, lap and unsupported measurements in random order. The desk-supported readings were the lowest, and the differences were big enough to reclassify a meaningful share of participants. That result is why any decent guide now says the arm must rest on a surface rather than being held. It also explains why so many people get a higher number at home than at the office, which reverses the usual white coat story described in the article on how to calm down blood pressure before a reading.
How to hold your arm when taking blood pressure
The honest answer is that you should not hold it at all. Holding involves muscle contraction, and a contracting muscle squeezes the vessels running through it, which pushes diastolic pressure up. Let the arm go completely slack on a table, palm facing up, elbow slightly bent, shoulder relaxed and dropped. If you can feel any effort anywhere in that arm, you are still holding it.
If your table is the wrong height, fix the table rather than your arm. A folded towel or a couple of books under the elbow costs nothing. People routinely improvise by propping the arm on a chair arm that sits four inches too low, which quietly biases every reading they will ever take. The same attention to setup shows up in the guide on getting an accurate reading at home, and it is the least glamorous, most effective thing on this page.
How to take blood pressure on the lower arm
People search for this meaning the forearm, and the answer is that a standard upper-arm cuff does not belong there. Forearm readings, taken over the radial artery below the elbow, exist as a fallback in hospitals when the upper arm cannot be used, and they read differently from upper-arm readings because the pressure wave amplifies as it travels outward. A forearm reading typically overstates systolic. If the upper arm is genuinely unusable on both sides, a validated wrist device used strictly at heart level is the more practical home option, with the accuracy limits set out in the piece on whether smart watches can measure blood pressure.
Arm height and heart level: the physics you cannot argue with
This is the one part of blood pressure measurement that behaves like a plumbing problem, because it is one. A column of fluid has weight. If your cuff sits below the level of your heart, the blood in the vessels between your heart and the cuff adds its own weight to the pressure the cuff measures, and the reading goes up. Raise the cuff above the heart and the same effect runs in reverse, so the reading falls.
Roughly 0.8 mmHg per centimeter of vertical displacement
Roughly 2 mmHg per inch
Cuff 4 inches below heart level = about 8 mmHg too high
Cuff 4 inches above heart level = about 8 mmHg too lowFour inches is nothing. It is the difference between an armrest and a dining table. It is the difference between resting your elbow on your thigh and resting it on a desk. Nobody watching would describe either posture as wrong, and yet one of them adds 8 mmHg to every reading you take.
Heart level means the middle of the cuff sits level with the middle of your sternum, roughly at the fourth intercostal space, which for practical purposes is mid-chest height when you are sitting upright. Not your shoulder. Not your elbow crease. The midpoint of the cuff itself. Measure it once against a mirror, note which surface in your home puts your arm there, and use that surface every time.
This is also the single biggest reason wrist monitors get a bad reputation. The device is not necessarily worse than an arm cuff. The problem is that a wrist naturally rests 8 to 12 inches below the heart when your hand is in your lap, which is exactly where people put it, producing readings 15 to 25 mmHg too high. Held correctly at chest height, a validated wrist monitor performs far better than its reputation suggests. That distinction between the device and the way people use it runs through the whole comparison of home monitor accuracy.
Worked example. Suppose your true seated pressure is 128/78. Take it with your arm in your lap, roughly 5 inches low, and you get about 138/86 once you also add the muscle effect of an unsupported limb. By US categories the first is elevated and the second is stage 1 hypertension. Run the mean arterial pressure on both and you get 78 + 50/3, about 95 mmHg, versus 86 + 52/3, about 103 mmHg. Neither number is dangerous, but only one of them is yours. The mean arterial pressure tool makes that comparison quick, and the article on whether 120/80 is actually good blood pressure explains why the boundaries between these categories are less clean than they look.
Lying down, sitting and standing: three different measurements
Can you take blood pressure lying down? Yes. Is it okay to take your blood pressure lying down? Also yes, with one condition: you have to know that you are producing a different measurement, not a more convenient version of the same one. Supine, seated and standing readings are three separate quantities and they should be logged separately.
Does lying down raise blood pressure?
The short version is that lying down usually nudges systolic pressure up slightly and pulls diastolic pressure down slightly compared with sitting. The mechanism makes sense. When you lie flat, blood that had been pooling in your legs returns to the chest, the heart fills more, and each beat ejects a bigger volume, which lifts the peak. At the same time your vessels relax a little, which softens the trough. The typical effect is in the range of a few mmHg either way rather than anything dramatic.
That is the average. Individual results scatter widely, and published studies genuinely disagree about the size and sometimes the direction of the shift, particularly for older adults and for people already on medication. Anyone who tells you supine is exactly 8 mmHg higher is quoting one study and ignoring the others. What is not in dispute is that the two positions are not interchangeable, so comparing Monday sitting against Tuesday lying and calling the difference a trend is meaningless.
There is an interesting wrinkle worth knowing. Research presented in recent years suggests that pressure measured while lying down may predict future cardiovascular risk at least as well as seated pressure, and possibly better, partly because it catches people whose pressure stays high when it should be falling. That does not make supine the new standard, and no major guideline has switched. It does mean supine readings are not a lesser measurement, just a different one.
How to take blood pressure lying down
The rules change slightly because heart level moves. Lie flat on your back with your head on a single low pillow. Put the cuffed arm at your side, resting on the mattress, and then support it with a folded towel or a pillow so that the middle of the cuff is level with the middle of your chest, which when you are supine means slightly raised off the bed rather than flat on it. An arm lying flat beside you sits below mid-chest level and will read a little high. Rest five minutes in that position before measuring, because moving from sitting to lying changes your pressure for the first few minutes.
Use a lying reading if you are ill, if standing or sitting up is difficult, or if a doctor has specifically asked for supine numbers. For routine home tracking, sitting is still the position that every reference range and every treatment threshold was built on, including the ones discussed in the guide to what counts as a good blood pressure number.
Can you take blood pressure standing up?
You can, and sometimes you should, but not as your default. Standing pressure is unstable for the first minute or two while your body compensates for gravity, so a standing reading captures a moving target. As a routine method it adds noise for no benefit.
As a deliberate test it is genuinely useful. Measuring seated or supine, then standing and measuring again at one and three minutes, is how orthostatic hypotension gets detected. That test matters most for older adults, for people on several blood pressure medications, and for anyone who feels lightheaded on standing, a symptom explored in the article on whether blood pressure medicine makes you dizzy.
What is a normal blood pressure while standing?
There is no separate normal range for standing, which surprises people. The published categories are all based on seated readings. What clinicians look at instead is the change. A small drop of a few mmHg on standing, recovering within a minute, is normal and expected. A sustained systolic fall of 20 mmHg or more, or a diastolic fall of 10 mmHg or more, within three minutes of standing meets the definition of orthostatic hypotension regardless of what the absolute numbers are. Someone can drop from 150/90 to 125/80 and be abnormal, while someone else sits at 105/65 standing and sitting alike and is fine, a picture the article on whether 100/70 is low blood pressure works through in detail.
Why blood pressure drops when you stand, and why it sometimes rises
Stand up and roughly half a liter of blood drops into the veins of your legs and abdomen within seconds. Less blood returns to the heart, so the next few beats eject less, and pressure falls. Your body notices almost immediately. Pressure sensors in the neck and chest signal the nervous system, heart rate rises, and the small arteries tighten. Within about thirty seconds a healthy system has clawed the pressure back, and most people never notice any of it.
What causes blood pressure to drop when standing in a way that you do notice? Usually one of these.
Dehydration or low blood volume
Less fluid in the system means less reserve to redistribute. This is the most common and most fixable cause, and the relationship between fluid intake and pressure is covered in the piece on whether drinking water affects blood pressure.
Medication
Diuretics, alpha blockers, nitrates and several others blunt the compensating response. Timing matters, and the drop is often worst in the couple of hours after a dose.
Nerve signaling problems
Diabetes, Parkinson disease and simple aging all reduce how fast the reflex fires. This is why orthostatic drops become more common with age.
Prolonged bed rest or a hot bath
Both leave vessels dilated and reflexes lazy, so the first stand is the worst one. Symptoms of a real drop are listed in the guide to the signs of low blood pressure.
Why does blood pressure increase when standing up in some people? Because the compensating response overshoots. The nervous system fires hard, vessels clamp, heart rate jumps, and diastolic pressure ends up higher standing than sitting. A rise in diastolic of around 5 to 10 mmHg on standing is entirely normal and is not a sign of anything. A large sustained rise, sometimes called orthostatic hypertension, is less common and is being studied as a possible marker of stiffer arteries. Either way, a modest upward move on standing is the usual pattern, not the alarming one.
Heart rate is the detail people miss when interpreting these tests. If pressure falls and heart rate climbs sharply, the system is responding, which usually points toward low volume. If pressure falls and heart rate barely moves, the reflex itself may be impaired, which is a more significant finding. That interaction is unpacked in the article on whether low blood pressure means a low heart rate, and the distinction between the two measurements is worth being clear about, as the explainer on whether bpm is the same as blood pressure spells out.
Leg and ankle blood pressure: a different test, not a substitute
Searches for how to check blood pressure in the leg usually come from one of two places. Either both arms are unusable, or somebody heard that a leg reading tells you something an arm reading cannot. Both are legitimate, and the answers are different.
Why is blood pressure higher in the legs than the arms?
Because the pressure wave amplifies as it travels away from the heart. Arteries get narrower and stiffer toward the periphery, and the reflected wave from the far end arrives earlier and stacks onto the forward wave. The result is that systolic pressure measured at the ankle is normally higher than systolic pressure measured at the upper arm in a healthy person, often by 10 to 20 mmHg. Thigh readings run higher too. Diastolic pressure changes much less along the way.
This is the part that trips people up. A leg reading of 150 systolic against an arm reading of 130 is not evidence of leg hypertension. It is the expected pattern. Legs reading the same as arms, or lower, is the finding that carries meaning, because it suggests something is obstructing flow into the leg.
What should ankle blood pressure be? The ankle-brachial index
The clinically useful version of an ankle reading is not the number itself but the ratio of ankle systolic to arm systolic. That ratio is the ankle-brachial index, and it is the standard screening test for peripheral artery disease. It is done properly with a handheld Doppler probe over the arteries at the ankle, with readings from both arms and both ankles, and the higher arm systolic used as the denominator.
ABI = highest ankle systolic on that leg divided by highest arm systolic
Example: ankle 140, higher arm 130, ABI = 140 / 130 = 1.08| ABI result | Interpretation |
|---|---|
| Above 1.40 | Arteries too stiff to compress, often from calcification. The test is not valid and another method is needed |
| 1.00 to 1.40 | Normal |
| 0.91 to 0.99 | Borderline |
| 0.90 or below | Consistent with peripheral artery disease |
Notice that this test needs the arm reading too, and specifically the higher arm reading, which brings the whole article full circle. The between-arm comparison you did at the start is a required input to the leg test. Notice also that a low ABI is a marker of arterial disease throughout the body, not just in the leg, which is why it correlates with the risks discussed in the article on what blood pressure level raises stroke risk.
How to take blood pressure on the ankle at home, and why you probably should not
Mechanically it is possible. You need a cuff sized for the ankle, wrapped just above the ankle bones with the tubing pointing up the leg, and the leg supported at heart level, which means lying flat rather than sitting. An automatic oscillometric monitor will usually produce a number.
The trouble is that the number is close to worthless on its own. Automatic monitors are validated on upper arms, and their algorithms assume the pulse waveform of a brachial artery. At the ankle, especially in someone with the arterial disease you might be trying to detect, those algorithms fail in ways that produce confidently wrong readings. A real ABI uses Doppler for exactly this reason. If a doctor asks you to take ankle readings at home for a specific reason, follow their instructions. Otherwise treat ankle numbers as a curiosity and keep tracking your arm.
If both arms are genuinely unavailable, a thigh or calf reading taken by a trained person with a correctly sized cuff is the standard fallback, and the results get interpreted with the amplification effect in mind rather than against arm reference ranges. That is a clinic job. Trying to reconstruct it at home with a supermarket monitor will give you numbers you cannot trust and cannot compare to anything, which is worse than not measuring. For everything else, the practical routines collected under the blood pressure section of the blog assume an upper-arm cuff for a reason.
Your measuring routine, start to finish
Everything above collapses into a short routine. Run it once to establish your arm, then run the shorter daily version forever.
Set up the room, not just the machine
You need a chair with a back and a table at roughly mid-chest height when you are seated. Test the height once with a tape measure against your sternum. If your dining table is too low, add a book. This one-time fix removes the most common source of error permanently.
Run the both-arms comparison once
Two readings per arm, alternating, averaged. Record both averages and the gap. Keep that note. If your gap is over 10 mmHg, repeat on a second day before you draw any conclusion.
Commit to the higher arm
Write left or right on the monitor case in permanent marker. Every future reading uses that arm. If you ever switch, note the date in your log, because otherwise a step change in your numbers will look like a health event when it was a wardrobe decision.
Sit for five minutes before every reading
Back supported, feet flat on the floor, legs uncrossed, bladder empty, no talking, no phone. This is the part everyone shortens and it is the part that matters most.
Position the cuff and the arm
Bare skin, snug enough that two fingertips slide under the edge with resistance, lower edge about an inch above the elbow crease, artery marker on the inside of the arm. Arm slack on the table, palm up, middle of the cuff at mid-chest height.
Take two readings a minute apart, and average them
If the two differ by more than 5 mmHg systolic, take a third and average the closest pair. A single reading is a snapshot with a lot of noise in it, and the reasoning behind averaging is set out in the guide on when to take a blood pressure reading.
Log the position alongside the numbers
Write seated, supine or standing next to every entry, along with the arm. A log without that context cannot be interpreted later, by you or by your doctor.
Judge yourself on the week, not the reading
Seven days of morning and evening readings, averaged, is what a diagnosis is actually made from. One high number on a Tuesday means very little, a point made repeatedly in the discussion of what level counts as high blood pressure.
If you are new to all of this, understanding what the two numbers represent makes the routine easier to stick to. The explainer on how blood pressure works and the short piece on what the top number means are the two worth reading first.
Common mistakes with arm choice and position
Switching arms without noticing. The classic version is measuring at home on one arm and at the pharmacy on the other, then wondering why the two disagree. They disagree because they are different arms. Always ask which arm was used when someone else takes your pressure.
Choosing the arm that reads lower because it looks better. Understandable and completely counterproductive. The lower arm is the one hiding information. Picking it does not lower your blood pressure, it only lowers your awareness of it.
Comparing arms on different days. Natural variation between days is larger than most between-arm differences, so a cross-day comparison measures the weather rather than your arteries. Compare within one sitting or not at all.
Measuring the same arm twice in a row without pausing. The second reading on a freshly squeezed arm runs low because the limb is still congested. Wait at least a minute, ideally two.
Holding the arm up instead of resting it. Muscle contraction raises diastolic pressure and the effect is not small. If your arm is doing any work at all, the reading is contaminated.
Using the armrest of a sofa. Sofa arms sit well below chest height for most people, which quietly adds several mmHg to every reading taken there. Dining tables are better than living rooms.
Treating a wrist device like an arm cuff. A wrist monitor resting in your lap will read dramatically high. Held at chest height with the forearm supported, it behaves far better.
Rolling a sleeve up into a tourniquet. A tight rolled sleeve above the cuff compresses the arm and distorts the result. Take the arm out of the sleeve or wear something short.
Measuring straight after activity, coffee or a cigarette. Every one of these shifts the number for half an hour or more, and the size of the effect is covered in the pieces on blood pressure after exercise and how coffee affects blood pressure.
Chasing a single alarming number. One reading of 158/96 taken with crossed legs in a lap-held cuff after a phone call is not a diagnosis. Fix the technique, repeat properly, then compare against the thresholds set out in the article on 140/90.
When a difference is worth a doctor visit
Most between-arm differences are noise. A few are not. This is the short list of things that deserve a conversation rather than another search.
A repeatable systolic gap of 10 mmHg or more. Not urgent. Bring it up at your next routine appointment with the actual numbers from at least two separate sessions. Your doctor will likely check pulses in both wrists and factor the gap into your overall cardiovascular risk.
A repeatable gap of 20 mmHg or more. Ask for this to be looked at properly. It raises the question of subclavian narrowing, which is investigated with ultrasound rather than guesswork.
One arm that feels cold, weak, numb or aches with use. A gap plus symptoms in the same limb is a much stronger signal than a gap alone.
Dizziness, fainting or falls on standing. Do the seated-to-standing test at home, write down the numbers and the timing, and take the log with you. This matters most for older adults and for anyone on multiple medications.
Any reading above 180 systolic or above 120 diastolic. Rest five minutes and repeat. If it stays that high, this is a hypertensive crisis and needs same-day medical attention. With chest pain, breathlessness, weakness on one side, slurred speech or vision loss, call emergency services immediately rather than repeating the reading. The thresholds and the reasoning behind them are set out in the article on the danger level for blood pressure.
A sudden large arm difference with severe chest or back pain. Rare, and an emergency. A new difference between arms accompanied by tearing pain can indicate a tear in the aorta. Do not measure again, call for help.
Readings that keep coming in very low with symptoms. Persistent numbers around or below 90/60 with fatigue, blurring or fainting deserve investigation, as discussed in the piece on whether 90/60 is low blood pressure.
Pregnancy. Arm consistency matters more here, not less, because treatment decisions move fast on small changes. Follow whatever protocol your clinic gives you, and see the notes on blood pressure during pregnancy for context.
Frequently asked questions
Which arm is best to check blood pressure?
The arm that reads higher on a proper side-by-side comparison. Measure both arms twice each in one sitting, average each side, and use the higher arm for every reading afterwards. If you have never done the comparison and need to pick today, use the right arm, because it reads slightly higher than the left in most people.
Does it matter what arm you take blood pressure on?
For most people the difference is 2 to 5 mmHg, which will not change anything. For roughly one adult in ten the gap is 10 mmHg or more, and for those people arm choice can decide whether a reading lands in the normal range or in a treatment category. You cannot tell which group you belong to without checking, which is why the one-off comparison is worth the ten minutes.
Should blood pressure be the same in both arms?
Close, but never identical. A few mmHg of difference is normal and largely reflects anatomy and measurement noise. A repeatable difference above about 10 mmHg systolic is the point at which current guidance suggests telling a doctor, and above 20 mmHg it warrants proper assessment.
Why is my blood pressure higher on my right arm?
Usually just your anatomy. The artery supplying the right arm branches off closer to the heart, and a small right-sided advantage is the normal pattern. If the right is higher by less than 10 mmHg, use the right arm and think no more about it. If it is higher by a lot, the question becomes why the left is low rather than why the right is high.
Can you take blood pressure on the right arm?
Yes. There is no rule against it and no accuracy penalty. The left arm is used in clinics because of how examination rooms are laid out, not because it is more correct.
Can you check blood pressure lying down?
Yes, and it is a valid measurement as long as you keep the arm supported at mid-chest level and label the reading as supine in your log. Do not compare a lying reading against a sitting reading and treat the difference as a change in your health.
Does lying down increase blood pressure?
Lying flat tends to raise systolic pressure slightly and lower diastolic pressure slightly compared with sitting, because more blood returns to the heart. The effect is usually a few mmHg. Studies disagree about the exact size, and in older adults the pattern is less predictable.
Is blood pressure higher when standing?
Diastolic pressure typically rises a little on standing while systolic dips briefly and then recovers. A sustained systolic fall of 20 mmHg or more within three minutes of standing is orthostatic hypotension and should be mentioned to a doctor, particularly if you feel lightheaded.
What causes blood pressure to drop when standing?
Blood pools in the legs when you stand, so less returns to the heart for the next few beats. Normally the nervous system corrects this within seconds. Dehydration, certain medications, prolonged bed rest, diabetes and aging all slow that correction, which is when the drop becomes noticeable.
How should I hold my arm when taking blood pressure?
You should not hold it at all. Rest it completely on a table, palm up, so that the middle of the cuff sits level with the middle of your chest. Holding the arm up involves muscle contraction, which pushes diastolic pressure up and makes the reading unusable.
What happens if my arm is below heart level?
The reading comes out too high, by roughly 2 mmHg for every inch the cuff sits below mid-chest height. An arm resting in your lap is often four or five inches low, which is enough to move a reading from one category to the next.
Which arm should I use with a pacemaker?
Use the opposite arm while the implant site is healing, which is usually a few weeks. After that either arm is fine. A blood pressure cuff does not interfere with a pacemaker electrically. Check with your cardiology team if you also have lines or leads they want protected.
Why is blood pressure higher in the legs than the arms?
The pressure wave amplifies as it travels toward the periphery, so ankle systolic normally sits 10 to 20 mmHg above arm systolic in a healthy person. A leg reading that matches or falls below the arm reading is the abnormal result, not the other way round.
How do I take blood pressure at the ankle, and what should it be?
A proper ankle measurement is part of the ankle-brachial index, done lying flat with a Doppler probe and compared against the higher arm reading. A ratio between 1.00 and 1.40 is normal, 0.90 or below suggests peripheral artery disease, and above 1.40 means the arteries are too stiff for the test to be valid. An ankle number taken alone with a home monitor is not reliable and should not be used as a substitute for an arm reading.
Can I take blood pressure on my leg at home if both arms are unavailable?
It is better than nothing but far from ideal, because home monitors are calibrated for the upper arm and their algorithms misread leg waveforms. If both arms are genuinely unusable, ask your doctor or nurse to establish a proper leg or thigh measurement protocol for you rather than improvising.
How often should I recheck both arms?
Once is usually enough unless something changes. Recheck if you get a new monitor, if you have arm surgery, if your readings shift for no obvious reason, or every couple of years as a matter of routine. Recording the result each time means you can see whether the gap itself is widening.
The short version worth keeping
Measure both arms once. Use the higher one forever. Write it on the monitor. That single decision removes a source of error most people carry for years without knowing it, and it costs you one session.
Then spend your attention on position, because position is where the bigger numbers hide. Back against the chair, feet flat, legs uncrossed, arm slack on a table at mid-chest height, five quiet minutes first, nothing said while the cuff inflates. Sitting for routine readings, lying down only when you have a reason and always labeled as such, standing only as a deliberate orthostatic test. Legs and ankles belong to a different test entirely, one that needs a Doppler probe and a ratio rather than a supermarket cuff and a hunch.
The between-arm gap is a small bonus finding that costs nothing to collect. Under 10 mmHg, ignore it. Over 10 mmHg twice, mention it. Over 20 mmHg twice, ask for it to be checked. That is the whole rule, and it is more than most people ever learn about their own circulation. For the tools and the wider set of guides, start from the waldev homepage and work outward, and keep the mean arterial pressure calculator handy for turning two numbers into the one figure that describes what your organs are actually being fed. If you want to see the same technique applied to interpreting a specific pair of numbers, the walkthrough on whether 112/75 is a good reading is a good next stop.
Related reading
Medical disclaimer and sources
Medical disclaimer. This article is general information about measurement technique and is not medical advice. It does not diagnose any condition and it is not a substitute for assessment by a qualified clinician. Never start, stop or change any medication based on a home reading or on anything written here.
Emergency thresholds. A reading above 180 systolic or above 120 diastolic, confirmed after five minutes of rest, is a hypertensive crisis and needs same-day medical care. If it comes with chest pain, difficulty breathing, weakness or numbness on one side, slurred speech, severe headache or loss of vision, call emergency services immediately.
Understanding blood pressure readings and correct measurement technique
