Introduction
Every log transaction – a storm-felled oak sold to a neighbor, a truckload of pine headed for the mill, a stack of cherry waiting on a portable sawmill – starts with the same question: how many board feet of lumber is actually in this wood? The industry answers with log rules: standard formulas that estimate board-foot yield from a log’s diameter and length. Doyle, Scribner, and the International 1/4-inch rule are the three standards, and they do not always agree.
The Log Board Feet Calculator runs all three scales from two inputs: the log’s small-end diameter inside the bark (inches) and its length (feet). It reports estimated board feet under each rule with metric equivalents, so you can compare scales side by side. This guide explains everything behind those numbers – what a board foot is, how each scale works, a full worked example, and the judgment calls the calculator cannot make for you.
What a Board Foot Is
A board foot (BF) is a unit of lumber volume equal to 144 cubic inches – a board 12 inches long, 12 inches wide, and 1 inch thick. Lumber is priced by the board foot, and logs are valued by the board feet they are expected to yield. One thousand board feet is abbreviated MBF, the standard unit for log and timber pricing. In metric terms, one board foot equals 0.0023597 cubic meters, and one MBF equals about 2.36 cubic meters.
Key Terms and Variables
Diameter (D)
The small-end diameter inside the bark, in inches. The diameter is taken at the narrow end of the log, excluding bark, because bark produces no lumber. Including bark inflates the estimate for no reason. For metric users, 1 inch equals 2.54 cm – a 16-inch log is about 40.6 cm across at the small end.
Length (L)
The log’s length in feet, usually in even-foot lengths (8, 10, 12, 16 ft) with trim allowance. For metric reference, 1 foot equals 0.3048 meters, so a 12-foot log is about 3.66 m long.
Log scale (log rule)
A standard formula that converts diameter and length into estimated board feet. The three rules disagree because they make different assumptions about saw kerf (wood lost to the blade), slab loss, and taper.
The Three Log Scales
Doyle
Doyle = (D – 4) squared x L / 16. The oldest and simplest rule, still standard for hardwood in much of the eastern US. Its known weakness: it underestimates small-diameter logs – heavily under about 16 inches – because the fixed 4-inch deduction for slab and edging is proportionally huge on a small log. Doyle returns zero or negative for diameters of 4 inches and under; that is a formula quirk, not a calculator error.
Scribner
Scribner = (0.79 x D squared – 2 x D – 4) x L / 16, the standard approximation of the Scribner Decimal C rule. Dominant for western softwood. It tracks actual mill recovery on small logs far better than Doyle. The formula approximates published tables, which can differ by a board foot or two on some sizes.
International 1/4-inch
International 1/4-inch = (0.04976 x D squared – 0.18573 x D – 0.01120) x L, using the standard published coefficients. Developed by the US Forest Service, it assumes a 1/4-inch kerf and accounts for taper, and is generally regarded as the most accurate of the three. Widely used for government timber sales. The full derivation is in the formula-explained guide.
How the Scales Compare
| Log (diameter x length) | Doyle (BF) | Scribner (BF) | International 1/4 in (BF) |
|---|---|---|---|
| 10 in x 8 ft | 18 | 28 | 25 |
| 12 in x 10 ft | 40 | 54 | 49 |
| 16 in x 12 ft | 108 | 125 | 117 |
| 20 in x 16 ft | 256 | 272 | 259 |
| 24 in x 16 ft | 400 | 403 | 387 |
Two patterns: Doyle penalizes small logs (18 vs 28 BF on a 10-inch log – a 35 percent haircut), and the scales converge on large logs (within a few percent at 24 inches). Scale choice matters most in the 10 to 18-inch range where small woodlots and yard trees usually fall – so always check which rule a buyer’s quote assumes.
Worked Example: A 16-Inch, 12-Foot Log
A full pass from measurements to board feet for a 16-inch diameter, 12-foot log (about 40.6 cm x 3.66 m), measured at the small end inside the bark:
Step 1 – Doyle. (16 – 4) squared x 12 / 16 = 144 x 12 / 16 = 144 x 0.75 = 108 BF.
Step 2 – Scribner. (0.79 x 256 – 32 – 4) x 12 / 16 = (202.24 – 36) x 0.75 = 166.24 x 0.75 = 124.68 BF, about 125 BF.
Step 3 – International 1/4-inch. (0.04976 x 256 – 0.18573 x 16 – 0.01120) x 12 = (12.73856 – 2.97168 – 0.01120) x 12 = 9.75568 x 12 = 117.07 BF, about 117 BF.
Step 4 – Metric. 108 BF x 0.0023597 = 0.255 cubic meters; 125 BF is about 0.295 cubic meters.
The spread – 108 to 125 BF for one log – is the whole story of log scaling in a single number. When money changes hands, confirm which scale the price assumes. For how prices attach to these numbers, see the cost guide.
Where This Number Gets Used
- Buying and selling logs: prices are quoted per MBF on a named scale – the scale changes the check.
- Portable sawmilling: estimating lumber yield before deciding a log is worth sawing.
- Timber sales: cruising and scaling standing timber to set sale prices.
- Project planning: even firewood and post projects start from knowing the wood in the log.
Measuring technique matters as much as the math: the estimating guide covers diameter and length readings the formulas can trust.
Mistakes That Distort Results
- Measuring outside the bark. Bark adds an inch or more and contains zero lumber. Always measure inside the bark.
- Measuring the big end. Every scale is defined on the small-end diameter; the large end inflates the estimate.
- Mixing units. Entering centimeters as inches (or meters as feet) produces a wildly wrong number that can look plausible.
- Treating Doyle as actual yield. On small logs Doyle is conservative by design – check which scale your buyer uses.
- Ignoring defects. Rot, sweep, and knots reduce real yield; the formulas assume a sound, straight log. See the material guide for defect deductions.
A fuller catalogue of these errors, with fixes, is in the common mistakes guide.
Related Guides
- Formula Explained – the Doyle, Scribner, and International 1/4-inch math derived step by step.
- Estimating Guide – how to measure diameter and length accurately in the field.
- Cost Guide – typical log prices per MBF and what moves them up or down.
- Pro Tips – practical advice for buying, scaling, and milling logs.
- FAQ – quick answers to the most asked log-scaling questions.
- Checklist – everything to verify before you buy, scale, or mill a log.
Frequently Asked Questions
What is a board foot?
A unit of lumber volume equal to 144 cubic inches – a board 12 x 12 x 1 inches. In metric, one board foot equals 0.0023597 cubic meters.
Which log scale should I use?
The one your market uses: Doyle for eastern US hardwood, Scribner for western softwood, International 1/4-inch for government sales. When you have a choice, International is generally considered the fairest estimate of actual recovery.
Why do the three scales give different numbers?
Different assumptions about saw kerf, slab loss, and taper. Doyle’s fixed 4-inch deduction punishes small logs; Scribner and International model small-log recovery more accurately.
Is the diameter measured inside or outside the bark?
Inside the bark, at the small end of the log. Bark contributes no lumber, and every scale is defined on the inside-bark, small-end diameter.
Can I use these numbers to buy or sell logs?
Yes, with cautions: confirm which scale the price is quoted on, scale each log yourself, and account for defects the formulas ignore. Consider hiring a professional scaler for commercial volumes.
Get Your Number
Log scaling is simple arithmetic built on careful measurement: small-end diameter inside the bark, length in feet, and the scale your market actually uses. The Log Board Feet Calculator does the arithmetic across all three rules – your job is the tape measure and the judgment about which rule applies. Run your logs, compare the scales, and confirm the scale with your buyer or mill before money changes hands.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Actual lumber recovery varies with species, log quality, defects, sawing method, and kerf. Verify volumes with your buyer, mill, or a professional scaler, and consult qualified professionals for timber-sale or structural decisions.
