Calculating board feet from a finished board is easy. Estimating how many board feet you will get out of a round, tapered, bark-covered log is a different and much more interesting problem, and it is the one that trips up first-time sawyers, firewood buyers eyeing a nice trunk, and anyone who has ever been offered “a truckload of logs” and had no idea what it was worth.
This guide walks through how log board-foot estimation actually works, why three competing “log rules” give three different answers, and how to read a real log the way an experienced sawyer does.
Why estimating a log is harder than measuring a board
A finished board is a neat rectangular solid. You measure its thickness, width, and length, and the amount of wood is settled. A log offers no such courtesy. It is round, usually tapered so one end is fatter than the other, and wrapped in bark that is not lumber at all. Worse, you cannot see inside it, so you do not know how much of the interior is sound wood and how much is rot, knots, or a hollow heart until the saw opens it up.
Because of all that uncertainty, nobody pretends to calculate the exact board footage of a log. Instead, the timber world uses estimation systems called log rules. A log rule is essentially a formula or lookup table that predicts how many board feet of lumber a log of a given diameter and length should produce once it is sawn. The prediction accounts for the wood inevitably lost to the saw blade, to slabs trimmed off the round sides, and to the general messiness of turning a cylinder into flat boards.
This is the key mental shift for anyone coming from board math. With a board, you calculate a fact. With a log, you produce an educated estimate, and the estimate depends on which log rule you use. Two honest people can look at the identical log, apply different rules, and quote board-foot figures that differ by a wide margin, without either of them being wrong. Understanding that is the first step to reading logs sensibly. If the very idea of a board foot as a unit still feels shaky, it is worth stepping back to our primer on what a board foot is before diving into log rules, because everything here assumes you already picture a board foot as a fixed block of wood. With that foundation in place, the leap from measuring a finished board to estimating a round log becomes far less bewildering, and the reason the rules exist at all snaps into focus.
The core idea: a log rule estimates the sawn lumber yield of a round log. It is a prediction, not a measurement, and different rules predict differently. That single sentence carries more weight than it first appears. It means that the phrase board feet, when applied to a log, is not a hard fact but a claim tied to a method. Ask what a board yields and there is one answer; ask what a log yields and the honest reply is always another question in return: by which rule? Holding that distinction firmly in mind will save you from a great deal of confusion the first time two quotes on the same log disagree.
What you actually measure on a log
Every log rule needs just two inputs, and knowing exactly how to take them is half the battle. Get these two measurements right and the rest is lookup or arithmetic.
Small-end diameter
You measure the diameter across the smaller end of the log, inside the bark. The small end is used because a tapered log can only yield full-length boards as wide as its narrowest point allows. Measuring inside the bark matters because bark is not lumber and including it would inflate the estimate.
Log length
You measure the usable length of the log in feet, typically rounding down to the nearest even foot or standard log length. Mills work in set lengths, and a log a few inches over a standard length rarely yields extra usable lumber, so the convention is to round down.
That is genuinely all a basic log-rule estimate requires: small-end diameter inside the bark, and length in feet. From those two numbers, each log rule produces its board-foot prediction, either through a formula or, more traditionally, by reading a value off a printed log-scale table or a scale stick held against the log end. The elegance of needing only two inputs is easy to overlook. A log is a complicated, irregular object, and yet centuries of practical experience have distilled its lumber potential down to two numbers anyone can take with a tape and a straight eye. That distillation is what makes log scaling learnable in an afternoon rather than a career, even though mastering its subtleties takes considerably longer.
It is worth stressing the small-end detail, because it is the single most common thing beginners get wrong. If you measure the big end of a fat, tapered log, you will badly overestimate its yield, since the full length of the log cannot produce boards as wide as that generous end. The narrow end sets the honest limit, so the narrow end is what you measure. This is not a matter of being conservative for its own sake. It reflects a physical truth about how boards come out of a log. A full-length board can only be as wide as the log allows along its entire run, and the tightest constraint sits at the small end. Any width the fat end offers beyond that is realized only in shorter pieces cut from the wider portion, which the basic rules do not fully credit. Measuring the small end keeps your estimate honest about full-length yield.
Measure the small end, inside the bark. Measuring the large end or including bark thickness are the two fastest ways to turn a fair estimate into a wildly optimistic one.
The three log rules, explained plainly
Three log rules dominate in practice, and each was built on slightly different assumptions about saw kerf, taper, and how a log breaks down into boards. You do not need to memorize their internal math, but you do need to know how they behave, because the difference between them is money.
The Doyle rule is simple and very widely used, especially in much of the eastern and southern United States. Its weakness is well known: it significantly underestimates the yield of small-diameter logs, because it assumes a generous slab loss on every log regardless of size. On big logs it is reasonably fair; on small ones it can shortchange the seller badly. Buyers often like Doyle for exactly that reason.
The Scribner rule was originally drawn up by diagramming how boards fit inside a circular log end. It generally lands between Doyle and International in its estimates and is common in the western United States. Because it was built from diagrams rather than a clean formula, it is traditionally read from a table, and a variant called Scribner Decimal C rounds values to the nearest ten board feet.
The International quarter-inch rule is widely regarded as the most accurate predictor of what a log will actually yield, because it was designed around a realistic quarter-inch saw kerf and accounts sensibly for taper. It is frequently used as the benchmark against which the other rules are judged. If you want the estimate closest to reality, International is usually the one to reach for.
The practical takeaway is that the same log scaled by Doyle, Scribner, and International will usually produce three different board-foot numbers, with Doyle typically lowest on small logs and International typically highest. None is a lie; they are three different lenses, and which one a buyer or seller prefers often depends on which side of the deal they are on. There is a certain wisdom in accepting this rather than fighting it. The rules are not competing attempts at the same truth that we simply have not resolved yet. They are deliberate conventions, each internally consistent, each favored in particular regions and particular trades for historical reasons. Your job is not to crown one as correct but to know which one governs the transaction in front of you and to reason accordingly.
The Doyle rule in practice
The Doyle rule has a clean formula, which is part of why it spread so widely before calculators and printed tables were common. It estimates board feet using the small-end diameter and the length like this:
Doyle board feet = ((Diameter − 4) ÷ 4)² × LengthWalk through a real log. Say you have a log sixteen inches across the small end and twelve feet long. Subtract four from the diameter to get twelve. Divide by four to get three. Square that to get nine. Multiply by the length, twelve, and you get one hundred eight board feet. That subtraction of four inches is the rule’s built-in slab allowance, and it is exactly why Doyle punishes small logs so heavily.
To see that punishment, shrink the log. Take an eight-inch log, twelve feet long. Eight minus four is four, divided by four is one, squared is one, times twelve is just twelve board feet. Compare that to what the same small log would truly yield and you can see why sellers of small-diameter timber tend to dislike Doyle intensely. The fixed four-inch deduction eats a huge fraction of a small log’s diameter.
When Doyle is used: it remains standard across many eastern and southern US mills, so if you are selling logs there, expect Doyle scaling and price accordingly. There is no use arriving at a mill in Doyle country insisting on International figures; the scale on offer is the scale you will be paid by. The productive response is to know in advance how Doyle treats your particular log sizes and to build that knowledge into the price you are willing to accept. A seller who understands the rule is never blindsided by the number on the scale sheet, even when that number feels low at first glance.
The Scribner rule in practice
Scribner is harder to reduce to a tidy formula because it grew out of physical diagrams of boards packed into a circle. In everyday use it is read from a log-scale table or a scale stick, where you cross-reference the small-end diameter with the length to find the board-foot value. That table-based nature is a feature, not a bug; it reflects the diagram-drawn origins of the rule.
For our sixteen-inch by twelve-foot log, a Scribner table typically returns a value noticeably higher than Doyle’s one hundred eight, because Scribner does not impose Doyle’s harsh fixed deduction. On small logs the gap is dramatic; on large logs the two rules move closer together. This is the pattern to remember: the rules diverge most on small logs and converge on large ones.
The Decimal C variant of Scribner, common in the western United States, simply rounds the tabulated board-foot figures to the nearest ten and drops the final digit, so a value of two hundred forty board feet is written as twenty-four. It is a bookkeeping convenience from the era of hand-tallied scale sheets, and it occasionally confuses newcomers who wonder why a big log scaled at “twenty-four.” Multiply the decimal figure by ten to recover the real board-foot count. Small quirks like this one are worth learning because they are exactly the sort of thing that makes a newcomer feel lost at a mill or an auction. Someone calls out a big log as scaling twenty-four, you picture two dozen board feet, and the mismatch with the obvious size of the log leaves you doubting your own judgment. Knowing the decimal convention dissolves the confusion instantly and lets you follow the tally with confidence.
The International 1/4-inch rule in practice
The International quarter-inch rule is the one to use when you want your estimate to track reality as closely as possible. It was derived to account for a realistic quarter-inch saw kerf and for the natural taper of a log along its length, which the simpler rules handle crudely or ignore. That care is why foresters so often treat it as the reference standard.
International is typically applied through a table as well, though it also has an underlying formula that estimates yield in four-foot sections and sums them, which is how it captures taper more faithfully than a single-diameter approach. For that same sixteen-inch by twelve-foot log, International generally returns the highest of the three estimates, reflecting its belief that a well-sawn log gives up more usable lumber than Doyle in particular assumes.
Here is how this plays out where it matters. If you are buying logs scaled by Doyle but you know International reflects true yield, you are effectively buying at a discount, since you will likely recover more lumber than the Doyle figure suggests. If you are selling, the opposite is true, and you would rather your logs be scaled by International or Scribner than by Doyle. None of this requires you to distrust anyone; it just requires you to know which rule is in play.
Reading three different log-scale tables by hand is a lot of work. You can estimate a log’s yield faster with the free Waldev board foot calculator, then compare it against the rule your buyer uses.
Comparing the three rules side by side
Numbers make the differences concrete. The table below shows rough, illustrative board-foot estimates for the same set of logs under each rule. Treat these as teaching figures that show the pattern rather than precise scale-table values, since exact tabulated numbers vary slightly by source.
| Log (small-end diameter × length) | Doyle (approx) | Scribner (approx) | International (approx) |
|---|---|---|---|
| 8 in × 12 ft | 12 | 28 | 35 |
| 12 in × 12 ft | 48 | 65 | 75 |
| 16 in × 12 ft | 108 | 125 | 140 |
| 20 in × 12 ft | 192 | 210 | 230 |
| 24 in × 12 ft | 300 | 320 | 340 |
Read across the small-log row and the point leaps out. On the eight-inch log, Doyle predicts a small fraction of what International does, a difference that would be infuriating to a seller. Now read down to the twenty-four-inch log and watch the three rules pull together. This is the single most important behavior to internalize: the choice of rule matters enormously for small logs and much less for large ones.
For anyone regularly trading logs near the small end of the range, this pattern is not academic. It is the difference between a fair price and being quietly shortchanged, purely through the choice of scaling rule. Knowing which rule applies, and roughly how far apart the rules sit for your typical log size, is a genuine financial skill in the timber trade.
Log board feet, lumber board feet, and linear feet all describe wood differently. Our breakdown of board foot vs linear foot untangles the units so you always know what a quote actually means.
Real-world estimation scenarios
Formulas and tables come alive when you attach them to actual situations. Here are four scenarios that show log estimation doing real work. Notice as you read them that the arithmetic barely changes from case to case; what changes is the decision riding on the number. The same small-end-diameter-and-length estimate serves a neighbor pricing a storm-felled tree, a hobbyist deciding whether a pile is worth milling, and a buyer choosing between two lots. That versatility is precisely why log scaling is such a foundational skill for anyone who works with round timber rather than finished boards.
Scenario one: pricing a single yard tree
A neighbor offers you a large walnut trunk that came down in a storm. It scales at twenty inches on the small end and ten feet long. Under Doyle that is roughly one hundred sixty board feet, under International closer to one hundred ninety. Before you agree on a price, you want to know which figure the deal is built on, because at walnut prices that thirty-board-foot gap represents real money. The estimate turns a vague “nice log” into a number you can negotiate with.
Scenario two: a portable sawmill hobbyist
A weekend sawyer with a portable band mill wants to know whether a pile of logs is worth the diesel and the day. Scaling each log and summing the estimates tells them roughly how many board feet the pile should yield, which they can weigh against the effort and the value of the lumber. Because band mills cut a thinner kerf than the rules assume, this sawyer often beats the International estimate, a pleasant surprise that Doyle scaling makes even more likely.
Scenario three: estimating a standing tree
Before felling, a landowner wants a rough sense of a standing tree’s lumber value. By estimating the usable log length and the small-end diameter of each merchantable section, they can apply a log rule to each section and total them. It is a rougher estimate than scaling a cut log, since the small-end diameter must be guessed, but it is enough to decide whether a tree is worth harvesting for lumber or is better left standing.
Scenario four: comparing two log lots
A buyer is offered two lots at the same total price: one of many small logs, one of fewer large logs. Scaling both lots reveals which actually contains more board feet. Because small logs scale so poorly under Doyle, the lot of large logs frequently wins on yield even when the piles look similar, a fact that only the estimate reveals.
Scaling a whole pile by hand is slow and error-prone. For a quick result across many logs, use the Waldev board foot calculator and total your estimates in a fraction of the time.
Where log estimates go wrong
Log scaling has a handful of classic pitfalls, and every one of them skews the estimate in a predictable direction. Knowing them lets you catch a bad number before it costs you. What unites these mistakes is that almost all of them push the estimate in the optimistic direction, inflating the apparent yield of a log beyond what it will truly give. That one-sided bias is worth remembering, because it means a careless estimate is far more likely to leave you disappointed at the saw than pleasantly surprised. Building the discipline to measure conservatively is the surest protection against paying for lumber that never materializes.
Measuring the large end. On a tapered log, the small end sets the yield limit. Measure the fat end and every estimate inflates, sometimes dramatically. Always scale from the narrow end.
Including bark in the diameter. Bark is not lumber. Measure the wood diameter inside the bark, or you will pay for material that ends up on the slab pile.
Ignoring defect. Rot, hollow centers, large knots, and ring shake all reduce real yield below any rule’s prediction. A rule assumes sound wood; a defective log will underperform its scale, and experienced scalers deduct for visible defect.
Forgetting which rule is in play. Quoting a Doyle figure while thinking in International terms, or vice versa, produces confusion and disputes. Always confirm the rule before you talk price.
Not rounding length sensibly. Mills cut standard lengths, so a log a few inches over a standard length rarely yields extra usable lumber. Round length down to the workable figure rather than counting every last inch.
Once you have a board-foot estimate, the next question is what it is worth. Our guide to lumber prices per board foot covers species values and the costly mistakes buyers make.
Using log estimates when you buy or sell
All of this theory earns its keep at the moment money changes hands. When you buy or sell logs, the estimate is your negotiating anchor, and understanding it protects you from paying for wood that is not there or selling wood for less than it is worth.
If you are buying, find out which rule the seller scaled by. If it is Doyle and the logs are small, you may be getting a genuine bargain on true yield, because Doyle understates small logs. If you are the seller of small logs, push for Scribner or International scaling, or price your Doyle logs knowing the rule works against you. Neither move is sharp practice; both are simply informed trading, and the party who understands log rules always has the advantage over the party who does not.
It also pays to remember that every rule is a prediction of sound wood sawn at an assumed kerf. Your actual results depend on your saw, your sawyer’s skill, and the hidden condition of each log. A thin-kerf band mill run by a careful operator can beat the International estimate, while a defective log full of rot will fall short of even a conservative Doyle figure. The estimate starts the conversation; the saw finishes it. It is a useful phrase to keep in mind whenever a scale figure starts to feel like a promise rather than a prediction. The number tells you what a typical sound log of that size ought to give under a stated set of assumptions. The actual boards stacking up beside the mill tell you what this particular log, with its particular flaws and this particular saw, truly held. Respecting the gap between those two things is the mark of an experienced hand.
Above all, treat the log rule as a decision tool rather than a guarantee. It exists to turn a round, unknowable object into a number you can plan and bargain with. Used that way, with clear eyes about its limits, it is one of the most useful skills anyone working with logs can carry.
Scale sticks, tables, and modern tools
For most of the history of the timber trade, log scaling was done with a physical scale stick. A scale stick is a flat measuring tool, held against the small end of a log, that reads the board-foot value directly for a given length once you line it up with the log’s diameter. Different sticks are printed for different rules and lengths, so a scaler in Doyle country carries a Doyle stick while one out west carries a Scribner stick. It is a beautifully simple instrument that turns a diameter into a board-foot estimate in a single glance.
Printed log-scale tables serve the same purpose on paper. You find the row for the small-end diameter and the column for the length, and the cell where they meet gives the estimate. These tables are where the Scribner and International values traditionally live, since neither reduces to a formula as cleanly as Doyle does. Foresters and buyers kept laminated versions in a pocket for decades, and many still do.
Today the same estimates are available without carrying a stick or a table at all. A calculator that knows the rules can take a diameter and a length and return the board-foot figure instantly, which is a real convenience when you are scaling many logs or want to compare what a single log yields under all three rules at once. The underlying logic has not changed since the scale-stick era; only the speed and the convenience have. Whichever tool you reach for, the two inputs remain the same trusted pair: small-end diameter inside the bark, and length in feet.
Worth knowing: a scale stick is printed for one specific rule. Reading a Doyle stick and calling the result International, or the reverse, is a common source of quoting errors, so always confirm which rule your stick or table represents.
Frequently asked questions
How do you calculate board feet in a log?
You estimate board feet in a log using a log rule, which predicts the sawn lumber yield from the log’s small-end diameter and its length. The three common rules are Doyle, Scribner, and International quarter-inch. Each takes the small-end diameter measured inside the bark and the length in feet, then returns a board-foot estimate through a formula or a scale table. The result is a prediction of yield, not an exact measurement, because a round log’s true output depends on the saw and the wood’s hidden condition.
Why do different log rules give different board foot numbers?
The rules were built on different assumptions about saw kerf, log taper, and how boards pack into a round log end. Doyle applies a large fixed slab deduction that heavily penalizes small logs, Scribner was drawn from board-packing diagrams and lands in the middle, and the International quarter-inch rule models a realistic kerf and taper for the most accurate estimate. Because their assumptions differ, the same log can scale to three different board-foot figures, with the gap largest on small logs and smallest on large ones.
Which log rule is the most accurate?
The International quarter-inch rule is generally considered the most accurate predictor of true lumber yield. It was designed around a realistic quarter-inch saw kerf and accounts for the natural taper of a log along its length, which the simpler rules handle crudely. Foresters often use it as the benchmark against which Doyle and Scribner are compared. For that reason, if you want your estimate to track reality as closely as possible, International is usually the rule to choose.
Do you measure the big end or the small end of a log?
You measure the small end of the log, inside the bark. A tapered log can only produce full-length boards as wide as its narrowest point allows, so the small end sets the honest limit on yield. Measuring the large end would badly overestimate the lumber the log can produce. Including bark thickness would also inflate the figure, since bark is not lumber, so the correct measurement is the wood diameter across the small end.
Why does the Doyle rule give such low numbers for small logs?
The Doyle rule subtracts four inches from the diameter before calculating, as a fixed allowance for the slabs trimmed off a log’s rounded sides. On a large log that deduction is a small fraction of the diameter, but on a small log it removes a huge share of the usable wood, driving the estimate far below reality. This is why sellers of small-diameter logs tend to dislike Doyle scaling and why buyers often prefer it. On large logs the rule is much fairer.
Can a sawmill get more board feet than the log rule predicts?
Yes, often. Log rules assume a particular saw kerf, and a thin-kerf band mill removes less wood per cut than the rules expect, so a careful operator can recover more lumber than the estimate suggests, especially against a conservative rule like Doyle. On the other hand, a log with hidden rot, a hollow center, or heavy knots can yield less than any rule predicts. The estimate is a starting point, and actual results depend on the saw and the wood’s true condition.
What is Scribner Decimal C?
Scribner Decimal C is a version of the Scribner rule that rounds board-foot values to the nearest ten and drops the final digit, so a log scaling two hundred forty board feet is written as twenty-four. It is a bookkeeping shorthand from the era of hand-tallied scale sheets and is common in the western United States. To recover the real board-foot figure, multiply the decimal value by ten. Newcomers sometimes find it confusing when a large log appears to scale at a small number.
How do I estimate board feet from a standing tree?
Estimate the usable log length and the small-end diameter of each merchantable section of the trunk, then apply a log rule to each section and add the results. Because you must estimate the small-end diameter before the tree is cut, this is rougher than scaling a felled log, but it is accurate enough to decide whether a tree is worth harvesting for lumber. Foresters use this approach to appraise standing timber before a single cut is made.
Put your log estimate to work
You now know how to read a log the way a scaler does: measure the small end inside the bark, note the length, pick a rule, and understand why that rule gives the number it does. That skill turns a round, uncertain object into something you can price and plan around with confidence. For a quick result on any log, run the numbers with the Waldev Board Foot Calculator — the guide explains the log rules, and the calculator helps you apply them fast. If you want to firm up the underlying math first, our primer on how to calculate board foot covers the formula in detail.
Disclaimer: The board-foot figures in this guide are illustrative estimates chosen to demonstrate how log rules behave, not precise scale-table values. Actual log scaling depends on the rule in use, local convention, visible defect, and the equipment doing the sawing. Always confirm the scaling rule and inspect logs for defect before buying or selling.
