How it works
A log rule is a formula or table that predicts how many board feet of lumber a log will yield. The rules disagree, sometimes by a lot, and each region and buyer tends to use one. Know which rule a buyer scales by before comparing bids.
Doyle is common in the South and parts of the Midwest and under-reads small logs on purpose. International 1/4-inch is the most accurate of the common rules and is the closest to real mill recovery. Scribner is also widely used, but I have left it out because the shortcut formulas for it do not match the published Scribner Decimal C table closely enough.
Worked example
A 16-inch small-end diameter log, 16 feet long. Published tables list 144 BF (Doyle) and 180 BF (International 1/4") for this log:
- Doyle = ((D − 4) ÷ 4)² × L = ((16 − 4) ÷ 4)² × 16 = 144 BF per log
- International 1/4": add 0.199 D² − 0.642 D for each 4-ft section, D rising 0.5 in per section:
- 40.7 + 43.6 + 46.6 + 49.7 = 180.6 BF per log
- International total = 181 BF
| Input | Value |
|---|---|
| Small-end diameter (inside bark) | 16 in |
| Log length | 16 ft |
| Number of logs | 1 |
| Result | Value |
|---|---|
| Doyle | 144 BF |
| International 1/4" | 181 BF |
| Doyle reads lower than International by | 20 % |
Assumptions and limits
- Diameter is measured inside bark at the small end, through the center. Round down to whole inches, as a scaler would.
- The result is gross scale. It does not deduct for rot, sweep, or defects; a scaler deducts those.
- International tables are printed rounded to the nearest 5 board feet, so this tool may differ from a printed table by a few board feet.
- The taper allowance in the International rule is 1/2 inch per 4 feet of length.
- Scribner is not included because no full published Scribner table was available to check a formula against.
Common questions
Why does Doyle give lower numbers than International?
Doyle subtracts 4 inches from the diameter to allow for slab and saw kerf, which hits small logs hardest. A 12-inch, 16-foot log scales 64 BF Doyle and about 95 BF International. The gap closes as diameter grows.
Which log rule should I use to sell timber?
Use whichever rule your buyer scales by. Ask before you sell, and convert each quote to the same rule to compare them fairly.
How do I measure log diameter?
Measure across the small end inside the bark, through the center, in inches. On an oval end, average the long and short diameters.
What does International 1/4-inch mean?
The rule assumes a 1/4-inch saw kerf. Its cousin, the International 1/8-inch rule, assumes a thinner kerf (band mills) and scales slightly higher.
Sources
- Doyle rule: standard forestry formula, BF = ((D − 4) ÷ 4)² × L.
- International 1/4-inch rule: J. C. Clark (1917); 4-foot section formula 0.199 D² − 0.642 D with 1/2-inch taper per 4 feet. Checked against the published 16-foot values (12 in = 95, 14 in = 135, 16 in = 180, 18 in = 230, 20 in = 290 BF, rounded to the nearest 5).
Updated 2026-09-30