Roof pitch is written as a ratio like 4/12 or 8/12, and if you are not in the building trade those numbers can look like a code. They are not complicated once you know the pattern. This guide explains what a 4/12 roof pitch is and walks through the other common ratios, showing what each number means, what the roof looks and feels like, its angle in degrees, and how to read any ratio you come across so you always know exactly how steep a roof is from its pitch alone.
What this guide covers
Every pitch ratio follows the same simple rule, so learning one teaches you all of them. Once the pattern clicks, a string like 7/12 tells you instantly how steep the roof is, and you can confirm any ratio, along with its angle and slope, in the Roof Pitch Calculator.
Type a ratio like 4/12 or 8/12 into the Roof Pitch Calculator and it shows the angle in degrees, the slope percentage, and the rafter multiplier. The guide below explains what the ratio itself is telling you.
How to read a pitch ratio
A roof pitch ratio is two numbers separated by a slash or the word in, such as 4/12 or 4 in 12. The first number is the rise, how many inches the roof climbs vertically, and the second is the run, how many inches it travels horizontally, which is almost always 12. So 4/12 means the roof rises 4 inches for every 12 inches it moves sideways toward the ridge. Read it as rise over run, and the steepness is simply the size of that first number.
Because the second number is fixed at 12, the ratio really has one variable, the rise, which is why comparing pitches is as easy as comparing the first numbers. A 4/12 is gentler than a 6/12, which is gentler than an 8/12, in the same order as 4, 6, 8. That is the entire logic of reading pitch ratios, and it is why what roof pitch is and this ratio guide together give you everything you need to interpret any pitch you meet, whether it appears on a plan, a quote, or a supplier’s spec sheet.
What the first number means
The first number, the rise, is the heart of the ratio because it alone sets the steepness. It is the inches of vertical climb per 12 inches of horizontal run, so a rise of 4 gives a gentle slope and a rise of 12 gives a steep one where the roof climbs as fast as it runs. Doubling the first number roughly doubles the steepness in feel, though not exactly in degrees, because the angle grows a little more slowly as the numbers climb.
Thinking of the first number as inches-of-rise-per-foot makes it concrete. A 6/12 roof gains half a foot of height for every foot you move toward the ridge, which is why it stands a fair way up over a wide house and gives usable attic space. A 3/12 roof gains only a quarter of a foot per foot, so it stays low. Once you read the first number this way, you can picture the roof from the ratio alone, and the rise, run and rafter guide shows how that rise scales up into a real roof height.
Why the second number is 12
The second number is the run, and it is 12 because North American roofing standardises pitch over a 12 inch run, one foot. Fixing the run at 12 lets every pitch be compared on the same base and makes the ratio easy to lay out with a framing square, which has the fixed 12 built in. It is the reason pitches are written over 12 and spoken with the 12 often dropped, as in a four for 4/12.
You will occasionally see the run written as something other than 12, usually when someone has measured over a different distance and not yet converted. To standardise it, divide the rise by the run and multiply by 12, which brings any measurement back onto the 12 base. But in normal use the second number is always 12, so when you read a ratio you can treat it as a given and focus on the first number for the steepness. The calculator handles any run and reports the standard over-12 form.
What a 4/12 roof pitch is
A 4/12 roof pitch rises 4 inches for every 12 inches of run. It is a gentle, low-to-moderate slope and one of the most common pitches on modern and ranch-style homes, partly because it is around the minimum pitch at which standard asphalt shingles are reliably watertight without special measures. As an angle it is 18.43 degrees, and as a slope it is 33.3 percent. From the street a 4/12 reads as a low, clean roof, not flat but not prominent, which suits contemporary designs.
Practically, a 4/12 is walkable with care, sheds water adequately but not aggressively, and offers limited attic headroom because it does not rise far. It is often the pitch chosen when a builder wants a modern look while staying within shingle requirements and keeping material and framing costs down. If your roof is a 4/12 and you are choosing a covering, check it against the shingle minimum in minimum roof pitch for shingles, since 4/12 is comfortably in shingle territory but shallower pitches are not.
What a 6/12 roof pitch is
A 6/12 roof pitch rises 6 inches per 12 inches of run, making it the classic medium pitch and probably the single most common residential slope. At 26.57 degrees and a 50 percent slope, it balances water and snow shedding, attic space, cost, and appearance about as well as any pitch can, which is why so many houses use it. It reads as a normal, comfortable roof, the shape most people picture when they imagine a house.
A 6/12 is walkable with reasonable care, sheds well, and gives usable attic headroom over a wide house because it stands a fair height. It is the default many builders reach for when there is no specific reason to go shallower or steeper, and it sits squarely in the conventional band where standard materials and methods all apply. If you are choosing a pitch and unsure, a 6/12 is a safe, all-round choice, as discussed in what roof pitch do I need.
What an 8/12 roof pitch is
An 8/12 roof pitch rises 8 inches per 12 inches of run, a moderately steep slope at 33.69 degrees and a 66.7 percent grade. It gives a taller, more traditional roof that sheds water and snow more aggressively than a 6/12 and creates more attic or vaulted-ceiling space. It is common on colonial and traditional homes and in climates with real snow, where the extra shedding earns its keep.
The 8/12 sits at the boundary of comfortable walkability; many people find it the steepest pitch they can work on without roof jacks or a harness, and beyond it a roof is generally treated as not walkable, as the walkable roof pitch guide explains. It costs a little more than a 6/12 in material and labour because the rafters are longer and the work slower, but it buys a stronger roof line and better shedding. An 8/12 is a good choice where snow, style, or attic space justify the extra steepness.
What a 3/12 roof pitch is
A 3/12 roof pitch rises 3 inches per 12 inches of run, a low slope at 14.04 degrees and 25 percent. It sits near the boundary between conventional and low-slope roofing, so it needs careful material selection: standard shingles may be marginal and often require extra underlayment protection, and below 3/12 many roofs move to low-slope systems entirely. A 3/12 reads as a distinctly low roof, common on porches, additions, and some modern homes.
Because it is close to the shingle limit, a 3/12 is a pitch to check carefully against material minimums before you cover it, using the minimum roof pitch guide. It sheds water slowly, so flashing and underlayment matter more than on a steeper roof, and it offers little attic height. Where a 3/12 is unavoidable, such as fitting an addition under existing windows, it works, but it demands more attention to waterproofing detail than a steeper pitch would, a theme covered in how to roof a low-pitch roof.
What a 12/12 roof pitch is
A 12/12 roof pitch rises 12 inches per 12 inches of run, meaning the rise equals the run and the roof sits at exactly 45 degrees, a 100 percent slope. It is the steep end of common pitches, giving a dramatic, tall roof that sheds snow and water very fast and creates generous vaulted space beneath. It is the signature pitch of A-frames and steep traditional and Alpine styles, where the roof is a defining feature of the building.
A 12/12 is not walkable without proper equipment, so working on one means roof jacks, staging, or a harness, and it costs more in both material and labour because the rafters are long and the work slow and careful. The steepness maximises shedding and drama but also wind exposure, which is why very steep roofs need robust fixings. A 12/12 is a deliberate choice for its look and its shedding, covered alongside other dramatic pitches in the A-frame and hip guide and the steep roof pitch guide. It is worth remembering that 12/12 is the point where the two words rise and run finally mean the same distance, which is a neat way to fix the idea that a 45 degree roof and a 12/12 pitch are one and the same.
What each ratio looks like
Connecting the numbers to appearance makes ratios intuitive. Under about 3/12 a roof looks nearly flat and modern. Around 4/12 to 5/12 it reads as a low, clean slope. A 6/12 looks like a normal, comfortable house roof. From 7/12 to 9/12 the roof becomes prominent and traditional, clearly a feature of the building. At 10/12 to 12/12 it is tall and dramatic, and past 12/12 it enters steep specialty territory like spires and Gothic forms.
This look-scale is why experienced builders can name a roof’s pitch by eye: they have connected the ratios to the shapes so often that the steepness reads at a glance. You can build the same instinct by comparing the ratios in this guide to roofs you see around you, checking your guesses against a measurement now and then. The angle chart pairs each ratio with its exact angle if you want to sharpen the connection between the number and the look.
The full ratio reference table
Here is every common ratio with its angle, slope, and a note on how it reads, so you can look up any pitch at a glance.
| Ratio | Angle | Slope % | How it reads |
|---|---|---|---|
| 2/12 | 9.46° | 16.7% | Nearly flat, low slope |
| 3/12 | 14.04° | 25% | Low, near shingle limit |
| 4/12 | 18.43° | 33.3% | Low-moderate, modern |
| 5/12 | 22.62° | 41.7% | Gentle suburban roof |
| 6/12 | 26.57° | 50% | Classic medium roof |
| 7/12 | 30.26° | 58.3% | Slightly steep |
| 8/12 | 33.69° | 66.7% | Traditional, steeper |
| 9/12 | 36.87° | 75% | Steep, roof jacks needed |
| 10/12 | 39.81° | 83.3% | Steep, prominent |
| 12/12 | 45° | 100% | Very steep, dramatic |
Reading down the table, notice how the angle climbs quickly through the low pitches and then slows, so the visual jump from 3/12 to 6/12 is larger than from 9/12 to 12/12. The slope percentage rises steadily to 100 at 12/12, where rise equals run. This one table lets you translate any common ratio into its angle, its slope, and its character, and the calculator extends it to any pitch, including the half pitches covered below.
Is a given ratio good?
People often ask whether a specific ratio is good, such as whether a 3/12 or a 4/12 is a good roof pitch. The truthful answer is that no ratio is universally good or bad; each suits certain purposes. A low pitch is good for a modern look and cost but poor for snow and attic space. A steep pitch is good for shedding, drama, and headroom but costs more and is harder to work on. Good depends on your climate, your material, your budget, and the look you want.
That said, some ratios are safer defaults. A 4/12 to 8/12 covers most houses well and keeps you within standard materials and methods. Below 3/12 you are into low-slope territory with special requirements, and above 12/12 into steep specialty roofing. So rather than asking if a ratio is good in the abstract, match it to your needs using what roof pitch do I need and check it against the material minimums in minimum roof pitch. The right ratio is the one that fits your roof’s job.
Half and fractional pitches
Not every roof is a whole number. Half pitches like 4.5/12 or 7.5/12 are real and used, often on additions designed to tuck under existing windows or to blend two roof lines. A half pitch reads exactly as its number suggests, sitting halfway between the two whole pitches around it, so a 4.5/12 is a touch steeper than a 4/12 and a touch gentler than a 5/12. You measure and describe it the same way, just with a fractional first number.
If you measure a roof and the reading lands between two whole numbers, it is either a deliberate half pitch, a slight measurement error, or a sag, so re-check before accepting it. For material ordering, use the exact fractional pitch, because the surface area depends on the true slope, and enter it in the calculator, which handles fractional pitches and returns the exact angle and multiplier. For framing, decide with the rest of the structure whether to build the half pitch or round to the nearest whole one.
Converting a ratio to degrees
Because ratios and degrees describe the same steepness, you will sometimes need to convert. The angle equals the arctangent of the rise over the run, which for the standard 12 base is the arctangent of the first number divided by 12. A 4/12 is arctan of 4 over 12, which is 18.43 degrees. You rarely need to do this by hand, since the ratio table above and the angle chart list the angle for every ratio, and the degrees guide explains the method.
Converting matters when a task uses degrees rather than the ratio, such as solar planning, setting a saw, or reading an international plan. Keeping the ratio and the degree value together, as in 6/12 which is 26.57 degrees, lets you speak to any trade without ambiguity. The calculator shows both at once, so once you have the ratio you have the degrees too, and the slope percentage alongside them. Fluency in all three forms is what lets you read any pitch specification with confidence.
Enter your ratio in the Roof Pitch Calculator for the angle, slope, and multiplier, then use the construction calculators to turn it into area and materials.
What a 2/12 roof pitch is
A 2/12 roof pitch rises 2 inches per 12 inches of run, a very low slope at 9.46 degrees and 16.7 percent. It sits at the boundary of low-slope roofing, right around the minimum for many shingle and metal panel systems, so it is a pitch where material choice becomes restrictive. Below 2/12 you are almost always into membrane or roll-roofing territory, and even at 2/12 the roof sheds water slowly and depends heavily on good underlayment and flashing to stay dry.
A 2/12 reads as nearly flat from the ground, giving a modern, horizontal look, and it appears on porches, additions, and contemporary homes. Because it is so close to the low-slope limit, it is a pitch to check carefully against the specific material minimum before covering, using the minimum roof pitch guide and, for metal specifically, minimum roof pitch for a metal roof. Where a 2/12 is used, treating it almost like a low-slope roof for waterproofing purposes is the safe approach, as covered in how to roof a low-pitch roof.
What a 5/12 roof pitch is
A 5/12 roof pitch rises 5 inches per 12 inches of run, a gentle-to-medium slope at 22.62 degrees and 41.7 percent. It sits comfortably between the low 4/12 and the classic 6/12, giving a suburban roof that is a little more pronounced than a 4/12 without the height of a 6/12. It is a common, unremarkable pitch that works well with standard shingles and most methods, and it reads as an ordinary, tidy house roof.
Because it is squarely in the conventional range, a 5/12 is walkable with care, sheds water well, and gives modest attic space. It is a frequent choice when a builder wants slightly more slope than a 4/12 for shedding or looks but does not need the full 6/12. If your roof measures 5/12, it is a versatile pitch with no special requirements, and any of the standard coverings in the minimum pitch guide will suit it. It is one of the safest all-round pitches you can have.
What a 7/12 roof pitch is
A 7/12 roof pitch rises 7 inches per 12 inches of run, a slightly steep slope at 30.26 degrees and 58.3 percent. It is a little steeper than the classic 6/12, giving a more pronounced roof that sheds snow and water a touch better and creates more attic height, while still being close to the everyday range. It reads as a moderately steep, traditional-leaning roof and is common where a builder wants a bit more presence or shedding than a 6/12.
A 7/12 is walkable with care by most people, though it is approaching the point where roof jacks become welcome, and it is the nearest standard pitch to a 30 degree roof, which is why it comes up in solar and international contexts. It costs marginally more than a 6/12 in material and labour because the rafters are slightly longer. If your roof is a 7/12, it is a solid, slightly steep pitch that suits snowier climates and traditional looks, sitting just below the walkability threshold discussed in the walkable roof pitch guide.
What a 10/12 roof pitch is
A 10/12 roof pitch rises 10 inches per 12 inches of run, a steep slope at 39.81 degrees and 83.3 percent. It gives a tall, prominent roof that sheds snow and water very effectively and creates generous vaulted or attic space. It is common on steep traditional styles and in heavy-snow regions, and it reads as a distinctly steep, dramatic roof that is a clear feature of the building.
A 10/12 is not comfortably walkable; working on one needs roof jacks, staging, or a harness, and it costs more in material and labour because the rafters are long and the work slow and careful, as the steep-roof working guide covers. The steepness maximises shedding and headroom but also wind exposure. If your roof is a 10/12, it is firmly in the steep category, and any work on it should treat access as a serious safety consideration rather than an afterthought.
What a ratio means versus what it looks like
People search both what a ratio means and what it looks like, and it is worth separating the two because they answer different questions. The meaning is the arithmetic: a 6/12 means 6 inches of rise per 12 of run, an angle of 26.57 degrees, a 50 percent slope. The look is the impression: a 6/12 appears as a normal, comfortable house roof. The meaning is exact and the look is a description, but together they let you both calculate with a ratio and recognise it in the world.
This is why this guide gives each ratio both its numbers and a note on how it reads. If you are estimating materials or framing, you use the meaning, feeding the exact ratio into the calculator. If you are trying to identify a roof or choose a look, you use the appearance. A question like what does a 4/12 pitch roof look like is really asking for the impression, which is a low, clean, modern slope, while what is a 4/12 roof pitch is asking for the meaning, 4 inches of rise per 12. Knowing which you need keeps the answer clear.
What a 9/12 roof pitch is
A 9/12 roof pitch rises 9 inches per 12 inches of run, a steep slope at 36.87 degrees and 75 percent. It gives a tall, traditional roof with strong shedding and plenty of vaulted or attic space, common on steep-climate and older homes. It reads as clearly steep and prominent, and it marks the point where a roof is generally treated as not walkable, so any work on it needs roof jacks, staging, or a harness. It costs more than a medium pitch because the rafters are long and the work careful.
The 9/12 is a popular choice where snow shedding and a strong roof line matter, sitting between the moderately steep 8/12 and the very steep 10/12. If your roof measures 9/12, it is a steep, capable roof that handles weather well but demands respect for access safety, as detailed in the steep roof pitch guide. It is also close enough to popular styling and snow-region norms that it appears frequently on traditional homes across colder parts of the country.
Comparing the common ratios side by side
Seeing the ratios in sequence makes their relationship clear. Moving from 2/12 up to 12/12, each step adds rise and steepness, but the effect is not even: the early steps from 2/12 to 6/12 change the look and behaviour a lot, moving from nearly flat to a normal roof, while the later steps from 9/12 to 12/12 change the numbers more than the impression, since the roof already looks steep. This is the tangent relationship at work, where equal jumps in rise produce shrinking jumps in angle.
Practically, this means the choice between a 4/12 and a 6/12 is a bigger decision than the choice between a 10/12 and a 12/12, both in looks and in the materials and methods that apply. The low-to-medium range is where most homes live and where the trade-offs are sharpest, while the steep range is more about style and shedding than everyday practicality. Keeping this pattern in mind helps you weigh a pitch choice sensibly, and what roof pitch do I need works through the decision in full.
Reading your own roof ratio
If you want to know your roof’s ratio, measure the rise over a 12 inch run using a level and tape on a rafter, or a safe no-climb method, and you have the pitch as a ratio directly. Enter it in the roof pitch calculator to confirm it and read the angle, slope, and rafter multiplier, turning the ratio into the working numbers you need. The measuring methods are all in how to calculate roof pitch.
From the ratio, the connected tools take over: roof area with pitch for materials, the rafter length guide for framing, and the minimum pitch guide for choosing a covering that suits your ratio. The roof pitch tool lives with the other estimators in the construction calculators category, near site tools like the dirt calculator, and the full roofing library is in the roof pitch blog off the homepage. Learn to read the ratio and you can size up any roof from two small numbers. From a single pair like 6/12 you can state the steepness, picture the roof, name its angle, judge whether it is walkable, and know roughly what it will cost to cover, which is a lot of understanding packed into two digits and a slash.
What is a 4/12 roof pitch: frequently asked questions
What is a 4/12 roof pitch?
A 4/12 roof pitch rises 4 inches for every 12 inches of horizontal run. It is a gentle, low-to-moderate slope common on modern and ranch homes, and it is around the minimum pitch at which standard asphalt shingles are reliably watertight without special measures. As an angle it is 18.43 degrees, and as a slope it is 33.3 percent. From the street it reads as a low, clean roof. It is walkable with care, sheds water adequately, and offers limited attic headroom because it does not rise far.
What does a 6/12 roof pitch mean?
A 6/12 roof pitch means the roof rises 6 inches for every 12 inches of run. It is the classic medium pitch and probably the single most common residential slope, balancing water and snow shedding, attic space, cost, and appearance. As an angle it is 26.57 degrees, and as a slope it is 50 percent. It reads as a normal, comfortable house roof, is walkable with reasonable care, and gives usable attic headroom over a wide house. It is a common default when there is no reason to go shallower or steeper.
What is an 8/12 roof pitch?
An 8/12 roof pitch rises 8 inches for every 12 inches of run, a moderately steep slope at 33.69 degrees and a 66.7 percent grade. It gives a taller, more traditional roof that sheds water and snow aggressively and creates more attic or vaulted-ceiling space. It is common on colonial and traditional homes and in snowy climates. It sits at the edge of comfortable walkability, so many people treat 8/12 as the steepest they will work on without roof jacks or a harness.
How do I read a roof pitch ratio?
Read it as rise over run. The first number is the rise, the inches the roof climbs vertically, and the second number is the run, the inches it travels horizontally, which is almost always 12. So 4/12 means the roof rises 4 inches for every 12 inches of run. Because the second number is fixed at 12, the steepness is set by the first number alone, so a 4/12 is gentler than a 6/12, which is gentler than an 8/12, in the same order as the numbers 4, 6, 8.
Why is roof pitch written over 12?
Because North American roofing standardises pitch over a 12 inch run, one foot. Fixing the run at 12 lets every pitch be compared on the same base and makes the ratio easy to lay out with a framing square, which has the fixed 12 built in. It is why pitches are written as a number over 12 and often spoken with the 12 dropped, as in a four for 4/12. If a run other than 12 is used, you divide the rise by that run and multiply by 12 to standardise it.
Is a 3/12 roof pitch good?
A 3/12 pitch is neither good nor bad on its own; it suits some purposes and not others. It gives a low, modern look and costs less to frame and cover, but it sheds water slowly, offers little attic height, and sits near the limit for standard shingles, so it needs careful material selection and extra underlayment protection. Below 3/12 many roofs move to low-slope membrane systems. A 3/12 works where a low roof is wanted or unavoidable, as long as the covering is rated for it and the waterproofing detail is right.
What does a 12/12 roof pitch mean?
A 12/12 roof pitch means the roof rises 12 inches for every 12 inches of run, so the rise equals the run and the roof sits at exactly 45 degrees, a 100 percent slope. It is the steep end of common pitches, giving a dramatic, tall roof that sheds snow and water very fast and creates generous vaulted space. It is the signature of A-frames and steep traditional styles. It is not walkable without roof jacks or a harness and costs more to build because the rafters are long and the work slow.
What is a half pitch like 4.5/12?
A half pitch is a roof whose rise is a fractional number of inches per 12 of run, such as 4.5/12 or 7.5/12. It reads exactly as the number suggests, sitting halfway between the two whole pitches around it, so a 4.5/12 is slightly steeper than a 4/12 and slightly gentler than a 5/12. Half pitches are real and used, often on additions that tuck under existing windows. For material ordering use the exact fractional pitch, since the surface area depends on the true slope, and the calculator handles fractional pitches directly.
Roofing safety and accuracy note: Roof work carries a real risk of falls. Only get on a roof when it is dry, the pitch is safe to walk on, and you use proper footwear and fall protection; when in doubt, hire a licensed roofer. The figures here are for general estimating and education and do not replace a structural engineer, a qualified roofer, or your local building code.
Model building codes set minimum roof slopes by material and require confirmation for your jurisdiction. International Code Council →
Roofing manufacturers publish the minimum pitch and installation rules their products are warranted for. Asphalt Roofing Manufacturers Association →