Board Foot CalculatorLog Board Feet Calculator
Enter the small end diameter inside the bark and the log length. See the board feet by the Doyle, Scribner and International 1/4 inch log rules side by side.
International 1/4 inch rule
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- Doyle
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- Scribner (formula)
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What is a log rule?
A log rule is a table or formula that estimates how many board feet of lumber can be sawn from a log. It uses the small end diameter inside the bark and the log length. The three rules in wide use in the United States are Doyle, Scribner and International 1/4 inch.
Purdue Extension notes that more than 95 log rules have been used in the United States and Canada, but only these three are widely recognized today [1]. A log rule is an estimate. Sawing method, kerf, log shape and defects all change the real yield [2].
Log rule formulas
Doyle = (D − 4)² × L ÷ 16
Scribner (Bruce and Schumacher fit) = (0.79D² − 2D − 4) × L ÷ 16
International 1/4 inch, per 4 ft section = 0.199D² − 0.642D
D is the small end diameter inside the bark in inches. L is the log length in feet. All three come from Purdue Extension publication FNR-191 [1].
- Doyle dates to the 1820s. It is the most common rule on private timber in the East and South. It under scales small logs and over scales large ones.
- Scribner is a diagram rule from 1846, based on fitting 1 inch boards into circles. The official Scribner Decimal C table rounds to the nearest 10 board feet and moves in uneven steps. This calculator uses the smoother formula fit published by Bruce and Schumacher, so expect small gaps from printed tables.
- International 1/4 inch was built by Judson F. Clark and changed to a 1/4 inch saw kerf in 1917. It assumes the log grows 1/2 inch in diameter every 4 feet. The calculator adds each 4 foot section and rounds to the nearest 5 board feet, as the rule does.
Which log rule should I use?
Use the rule your buyer or mill uses, since prices are set per thousand board feet under one rule. For the closest estimate of real lumber yield, the International 1/4 inch rule is usually preferred. Doyle is common in timber sales in many eastern and southern states, so sellers should know both.
Ohio State Extension reports that Doyle is the most common rule in Ohio, while state agencies and the U.S. Forest Service use the International 1/4 inch rule [2]. Missouri Extension names the same two as the most used in Missouri [3].
How to measure a log
- Measure the length with a tape. Being a few inches short of a full foot drops the log to a shorter length class.
- At the small end, measure the diameter inside the bark twice, at right angles. Average the two numbers.
- Scale logs over 20 feet as two or more shorter logs.
- Reduce the length or volume for rot, splits, sweep and crook.
These steps follow Purdue Extension FNR-191 [1].
Doyle log scale chart
| Diameter (in) | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft |
|---|---|---|---|---|---|
| 8 | 8 | 10 | 12 | 14 | 16 |
| 10 | 18 | 23 | 27 | 32 | 36 |
| 12 | 32 | 40 | 48 | 56 | 64 |
| 14 | 50 | 63 | 75 | 88 | 100 |
| 16 | 72 | 90 | 108 | 126 | 144 |
| 18 | 98 | 123 | 147 | 172 | 196 |
| 20 | 128 | 160 | 192 | 224 | 256 |
| 22 | 162 | 203 | 243 | 284 | 324 |
| 24 | 200 | 250 | 300 | 350 | 400 |
| 26 | 242 | 303 | 363 | 424 | 484 |
| 28 | 288 | 360 | 432 | 504 | 576 |
| 30 | 338 | 423 | 507 | 592 | 676 |
| 32 | 392 | 490 | 588 | 686 | 784 |
| 36 | 512 | 640 | 768 | 896 | 1,024 |
| 40 | 648 | 810 | 972 | 1,134 | 1,296 |
Doyle, Scribner and International compared
| Diameter (in) | Doyle | Scribner (formula) | International 1/4 |
|---|---|---|---|
| 8 | 16 | 31 | 40 |
| 10 | 36 | 55 | 65 |
| 12 | 64 | 86 | 95 |
| 14 | 100 | 123 | 135 |
| 16 | 144 | 166 | 180 |
| 18 | 196 | 216 | 230 |
| 20 | 256 | 272 | 290 |
| 22 | 324 | 334 | 355 |
| 24 | 400 | 403 | 425 |
| 26 | 484 | 478 | 500 |
| 28 | 576 | 559 | 585 |
| 30 | 676 | 647 | 675 |
| 32 | 784 | 741 | 770 |
| 36 | 1,024 | 948 | 980 |
| 40 | 1,296 | 1,180 | 1,215 |
On a 12 inch log, Doyle gives about two thirds of the International value. The gap closes as logs get bigger, and Doyle passes the other rules on very large logs.
What is overrun?
Overrun is the lumber a mill saws beyond the log scale. Purdue Extension gives it as: overrun % = (lumber tally ÷ log scale − 1) × 100 [1]. Doyle often shows overrun on small logs because it under scales them. To measure sawn boards, use the board feet calculator.
Questions
What is the Doyle log rule formula?
Doyle board feet = (D minus 4) squared × L ÷ 16. D is the small end diameter inside the bark in inches. L is the log length in feet. A 20 inch log 16 feet long holds 256 board feet by Doyle.
Which log rule is most accurate?
Purdue Extension calls the International 1/4 inch rule probably the most accurate of the three, since it is based on a study of sawing losses and allows for log taper. Ohio State Extension says it is the best estimate of what can be sawn from a log under good conditions.
Why does Doyle give such low numbers for small logs?
Doyle takes 4 inches off the diameter for slabs and edgings before it squares the result. That cut is too large for small logs and too small for big ones. So Doyle under scales small logs and over scales large logs, according to Purdue Extension.
Where do I measure the diameter of a log?
Measure at the small end, inside the bark. Logs are rarely round, so Purdue Extension advises measuring two diameters at right angles and averaging them. Measure length with a tape, not by eye.
How do I scale a log longer than 20 feet?
Under the International 1/4 inch rule, logs over 20 feet are scaled as two or more shorter logs. Measure the small end diameter of each section and add the results.