How to use the log board foot scale calculator
- Enter the small-end diameter of the log, inside the bark, in inches.
- Enter the length in feet and how many logs of that size you have.
- Open More options to change the taper used by the International rule.
- Compare the two rules and look up neighboring diameters in the table.
Formula
Doyle: board feet = (D - 4)^2 x L / 16
International 1/4 inch: each 4 foot section of diameter d holds 0.22 d^2 - 0.71 d board feet
The diameter grows by the taper (0.5 inch) for each next 4 foot section
A last section shorter than 4 feet is prorated
D is the small-end diameter in inches inside the bark and L the length in feet. A board foot is a board 1 foot long, 1 foot wide and 1 inch thick.
Three logs
A 16 inch log 16 feet long scales 144 board feet by Doyle, because (16 - 4)^2 x 16 / 16 = 144. By the International rule its four sections are 44.96, 48.18, 51.51 and 54.95 board feet, a total of 199.6, which matches the published figure of 200. Doyle comes out 27.9 percent lower.
A 12 inch log 8 feet long scales 32.0 by Doyle and 48.7 by the International rule, and a 24 inch log 12 feet long scales 300 and 344.1. The gap between the rules is widest for small logs.
Why the rules disagree
A log rule is a formula that estimates the lumber a log will yield. Doyle subtracts 4 inches from the diameter to allow for slabs and kerf, which suits large logs but gives too little for small ones, so buyers who scale by Doyle pay by a smaller number on small logs. The International rule is built from the lumber that can actually be sawn from a series of 4 foot sections, so it follows the real yield better across sizes.
For lumber you already have, use the board foot calculator and the nominal to actual lumber size converter. To plan cuts see the cutting stock board optimizer, and for metal parts the metal weight calculator.
What scaling does not tell you
Both rules are estimates. Sweep, rot, knots, the sawing pattern and the mill's kerf all change the real yield. The published International tables round to the nearest 5 board feet, so the formula result may differ slightly from a table. The Scribner rule, common in some regions, uses a table rather than a formula and is not included here.
Assumptions and limits
- Diameter is measured inside the bark across the small end, in whole or fractional inches.
- Log lengths run from 1 to 60 feet. Logs are treated as straight, with a steady taper.
- The International rule is the 1/4 inch kerf version, applied by 4 foot sections with a taper of 0.5 inch per section as an editable default.
- Defects are not deducted, so the numbers are gross scale.
Frequently asked questions
How many board feet are in a log?
It depends on the rule. A 16 inch log 16 feet long is 144 board feet by Doyle and about 200 by the International 1/4 inch rule. The page shows both.
What is the Doyle log rule?
Doyle estimates board feet as the square of the small-end diameter less 4 inches, times the length in feet, divided by 16. It is simple but underestimates small logs.
What is the International rule?
It estimates the board feet in each 4 foot section from the diameter, using 0.22 d^2 minus 0.71 d, and adds the sections with the diameter growing along the log. It is based on sawn lumber and is the more accurate of the two.
Which rule does a buyer use?
It varies by region and mill. Ask the buyer which rule and which defect deductions apply, because the price per board foot only makes sense with the rule.