Log Scale Calculator

How to calculate board feet in a log

1. Measure the small end of the log, inside the bark, and round down to the whole inch.
2. Measure the length in feet, without the trim allowance (the extra 3–6 inches left for squaring the ends).
3. Pick the log rule your buyer or seller uses — Doyle, Scribner or International ¼ — and read the board feet from the calculator above or the log scale chart below.

A log rule does not measure the wood in a log — it estimates how many board feet of lumber a mill will saw out of it. Each rule makes its own assumptions about saw kerf, slabs and taper, so the same log scales differently.

Doyle log rule

Board feet = ((D − 4) ÷ 4)² × L, where D is the small-end diameter in inches and L is the length in feet. Doyle takes 4 inches off the diameter for slabs, which hurts small logs badly: a 12-inch, 16-foot log scales 64 board feet by Doyle against 97 by International ¼. Doyle is still the most common rule for hardwood sawlogs in the South and Midwest — if you buy logs by Doyle, small logs give you a big overrun; if you sell them, you are paid for less than you deliver.

Scribner log rule

Scribner (1846) was drawn from diagrams: circles for the log ends, 1-inch boards with a ¼-inch kerf fitted inside. It is the standard in the western US and on most federal timber sales there, often as Scribner Decimal C (rounded to tens of board feet). The calculator uses the formula form (0.79·D² − 2·D − 4) × L ÷ 16, which follows the diagram rule within a few percent — it is not the official Scribner table, so use the official table when a contract names it.

International ¼-inch log rule

International ¼ (Judson Clark, 1906) is the closest to what a careful mill actually saws. It assumes a ¼-inch kerf and adds ½ inch of diameter for every 4 feet of length to account for taper. Per 4-foot section it uses 0.22·D² − 0.71·D (for an ⅛-inch kerf) and then multiplies by 0.905. The US Forest Service and many eastern states use it for timber cruising.

Doyle vs Scribner vs International

On small logs Doyle gives the least, International the most. The gap closes as logs get bigger: on a 16-foot log Doyle catches up with Scribner at about 25 inches and with International ¼ at about 30 inches. Before you agree on a price, agree on the rule.

How many board feet are in a log?

• A 12-inch, 16-foot log: 64 board feet by Doyle, 86 by Scribner, 97 by International ¼.
• A 16-inch, 16-foot log: 144 board feet by Doyle, 166 by Scribner, 181 by International ¼.
• A 20-inch, 16-foot log: 256 board feet by Doyle, 272 by Scribner, 290 by International ¼.
• A 24-inch, 16-foot log: 400 board feet by Doyle, 403 by Scribner, 424 by International ¼.

Other sizes are in the chart below; for a whole truckload, tally the logs in the log load calculator.

Overrun: when the mill beats the scale

Overrun is the lumber you actually saw minus the log scale, in percent of the scale. Doyle overruns are often 20–50% on small logs; International ¼ overruns are small. To see what a log really gives with your board sizes and kerf, run it through the log cutting calculator — it draws the pattern and shows the overrun against Doyle and International ¼. Need board feet of sawn lumber instead? Use the board foot calculator.

By Ivan Lukichev, former band-sawmill operator. Rules: Doyle and International ¼ by their formulas; Scribner by the formula approximation of the diagram rule.