Log Board Foot Calculator

Why the Same Log Gets Three Different Answers

A log doesn't come with a board-foot number stamped on the end. What a mill actually saws out of it depends on kerf width, slabbing losses, taper, and how the sawyer lays out the cuts — none of which a simple diameter-and-length measurement can capture on its own. Rather than chase an exact figure no two mills would agree on anyway, foresters settled decades ago on standardized log-scaling rules that estimate yield closely enough for buying, selling, and mill-tally purposes. Doyle (an 1837 formula still standard through the eastern and southern U.S.), Scribner (built from diagrams of boards packed inside circles, common on western and public timber sales), and the International 1/4-inch rule (developed in 1917 by the U.S. Forest Products Laboratory specifically to correct Doyle's known bias) don't agree with each other by design — each was calibrated around different assumptions about kerf and slabbing loss. Which one is "right" depends on which rule the buyer, seller, or mill you're dealing with actually uses.

Measuring a Log Correctly

All three rules need the same two measurements: small-end diameter inside the bark, and length rounded down to the nearest standard even foot (8, 10, 12, 14, and 16 ft are typical sawlog lengths). The most common measuring mistake is calipering across the bark rather than the wood underneath it — bark can add half an inch or more per side on some species, enough to noticeably inflate the estimate. The second is measuring the large end instead of the small end; scaling always uses the small end, because that's the diameter that actually limits how wide a board the log can produce.

Doyle, Scribner, and International 1/4″ — How Each One Works

Doyle's formula, (D − 4)² × L ÷ 16, subtracts a flat 4 inches from the diameter before squaring, as a rough stand-in for slabbing loss — simple, but that flat subtraction is oversized relative to small logs, which is why Doyle systematically underestimates yield as diameter drops. Scribner has no clean algebraic formula at all; it was originally built by literally drawing 1-inch boards inside circles of each diameter and counting them, so real Scribner values come from a lookup table. This calculator uses a widely published polynomial approximation of that table, (0.79D² − 2D − 4) × L ÷ 16 — close to the official numbers but not identical, since it's fitting a curve to a table rather than reproducing it exactly. The International 1/4" rule takes a different approach entirely: it models the log's taper explicitly, assuming the diameter grows by about half an inch every 4 feet moving away from the small end, and calculates yield section by section (with a 1/4-inch saw kerf built in) rather than once for the whole log. That extra care is why foresters and the USDA Forest Service generally regard it as the most accurate of the three for actual sawn yield, even though Doyle remains the everyday standard for buying and selling timber in much of the country.

A 16-Inch, 16-Foot Log Worked Out

Take a log with a 16-inch small-end diameter and a 16-foot length. Doyle gives (16 − 4)² × 16 ÷ 16 = 144 board feet. The International 1/4" rule, summed across four 4-foot sections with the taper allowance applied, comes out to roughly 181 board feet. Scribner's approximation lands in between, around 166 board feet. That's nearly a 25% spread between the lowest and highest estimate for the identical log — and the gap isn't a rounding quirk, it's the direct result of the three rules encoding different assumptions about how much wood is lost to kerf, slabs, and taper. The gap narrows on larger, straighter logs and widens further on smaller ones, which is exactly the pattern that exposes Doyle's weakness at the low end.

Where These Rules Fall Apart

Doyle's formula squares (D − 4), which is mathematically fine down to a 4-inch diameter, where it bottoms out at zero — but below 4 inches, the squared term starts climbing again as diameter keeps shrinking toward zero. Taken literally, that would mean a 2-inch log yields more lumber than a 3-inch one, which is nonsense. Because of that, this calculator doesn't display a Doyle figure at all for logs under 4 inches; there's no meaningful number to show, only a formula behaving badly outside the range it was built for. Diameters under about 6 inches also fall outside the range published log-scale tables normally cover, so results down there are extrapolated from the algebraic formulas rather than drawn from real table data, and get more approximate the smaller the log gets. All three rules also assume a straight, evenly tapered, round log — a crooked, forked, or heavily tapered log will scale lower in practice than any of these formulas predict. Treat every result here as an industry-standard planning estimate, not a substitute for an actual mill tally once the log is on the deck.