Doyle log scale
The Doyle log scale is the simplest and most widely used log rule in the eastern and southern US: subtract 4 in from the small-end diameter, square it, multiply by the length in feet and divide by 16[1]. Its weakness is small logs, where it can show only a fraction of the lumber a mill recovers.
| Small-end diameter | Doyle | International 1/4″ | Doyle as % of International |
|---|---|---|---|
| 8 in | 16 | 40 | 40% |
| 10 in | 36 | 65 | 55% |
| 12 in | 64 | 95 | 67% |
| 14 in | 100 | 135 | 74% |
| 16 in | 144 | 180 | 80% |
| 18 in | 196 | 230 | 85% |
| 20 in | 256 | 290 | 88% |
| 22 in | 324 | 355 | 91% |
| 24 in | 400 | 425 | 94% |
| 28 in | 576 | 585 | 98% |
| 32 in | 784 | 770 | 102% |
International 1/4-inch rule
The International rule was built from the actual sawing of a log into boards with a 1/4 in saw kerf, and is the most accurate of the common rules, though less used in trade. Purdue gives a formula for each length (for a 16 ft log, 0.796D² − 1.375D − 1.230) and Grosenbaugh's single formula for any length up to 20 ft, rounded to the nearest 5 board feet[1]. Longer logs are scaled as two logs.
How to measure a log for scaling
- Diameter: at the small end, inside the bark, in inches; average two measurements at right angles on an oval log.
- Length: in feet, usually with a few inches of trim allowance left on the log.
- Sawn lumber is then tallied with the board foot calculator, and its weight comes from the lumber weight calculator.
Frequently asked questions
How do you calculate board feet in a log?
With a log rule. Doyle: (D − 4)² × L ÷ 16, using the small-end diameter inside the bark in inches and the length in feet. A 16 in, 16 ft log scales 144 board feet.
What is the Doyle log scale?
A formula rule, board feet = (D − 4)² × L ÷ 16, widely used for buying and selling logs in the eastern US. It underestimates small logs.
Which log scale is most accurate?
The International 1/4-inch rule is considered the most accurate of the common rules across log sizes.
Is this a log scale calculator?
Yes. It scales a log by the Doyle and International 1/4-inch log rules from the small-end diameter and the length.