What a log rule does
A log rule is a formula or table that predicts the board feet a log will saw into. It cannot know the knots inside, so it estimates from the small-end diameter and the length. Different rules assume different amounts of waste, so the same log can scale differently depending on who buys it.
Doyle
Board feet = (diameter − 4)² ÷ 16 × length (ft)
Doyle subtracts 4 inches for slabs and kerf. It is the common rule for hardwood logs in much of the eastern US, and it under-scales small logs, so sawmills that buy on Doyle often get more lumber than the scale shows.
International 1/4 inch
Per 4 ft section = 0.905 × (0.22D² − 0.71D), with the diameter growing 1/2 inch per section
The International rule allows a 1/4 inch saw kerf and 1/2 inch of taper for each 4 feet of length. It is closer to what a mill actually recovers, especially in small logs. This calculator uses the formula, so its results can differ from a published table by a few board feet, because tables are rounded.
16 ft logs, by diameter
Values from the formulas used here. The published Extension table for 16 ft logs gives 36, 64, 144 and 256 for Doyle, and 65, 95, 180 and 290 for International 1/4 inch, at 10, 12, 16 and 20 inches.
| Small-end diameter | Doyle | International 1/4 | Difference |
|---|---|---|---|
| 10 in | 36 | 65 | +80% |
| 12 in | 64 | 97 | +51% |
| 14 in | 100 | 136 | +36% |
| 16 in | 144 | 181 | +25% |
| 18 in | 196 | 232 | +18% |
| 20 in | 256 | 290 | +13% |
| 24 in | 400 | 424 | +6% |
Note how much Doyle undercounts small logs: at 10 inches it reads about half of the International figure, and at 24 inches the two are close. The rule you are paid on matters more than the log's exact diameter.
To weigh the log for hauling, use the log weight calculator. For finished boards, use the board foot calculator.
Frequently asked questions
How many board feet are in a log?
It depends on the rule. A 16 inch by 16 ft log is 144 board feet by Doyle and about 181 by the International 1/4 inch rule.
Which log rule is most accurate?
The International 1/4 inch rule is generally closest to what a mill recovers, especially in small logs. Doyle under-scales small logs.
Where do I measure the log diameter?
At the small end, inside the bark, across the narrowest line.
Sources
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