How to Estimate Board Feet in a Log Before You Mill It

There is a moment before a log hits the mill when a simple question decides whether the day pays for itself: how many board feet are actually inside it? Guess high and you overpay for logs or promise lumber you cannot deliver. Guess low and you leave money on the landing. Log scaling is how you answer that question before the saw ever runs.

The good news is that scaling a log takes two measurements and one lookup. The catch is that the answer depends on which log rule you use, and the three common rules can disagree by a wide margin on the same log. This guide walks through the measurements, the rules, and how to read the result without kidding yourself.

The two measurements you need

Every log rule works from the same two numbers, so start here.

The first is the small-end diameter, measured inside the bark. A log tapers, so the narrow end sets the limit on the boards you can saw the full length. Measure across the small face inside the bark, and if the end is oval, take the shortest and longest widths and average them. Round down to the nearest inch, the way scalers do, because bark and rot at the edge do not turn into lumber.

The second is the log length in feet. Most mills scale in even two-foot steps and add a few inches of trim allowance, so a log cut at 8 feet 4 inches is scaled as an 8-foot log. The extra is there to square the ends, not to yield boards.

That is the whole field measurement. Small-end diameter inside the bark, and length in feet. Everything after that is choosing a rule and reading a number, which the log scale calculator does for you the moment you type those two figures in.

Why there are three log rules

A log rule is just a table or formula that estimates the board feet of finished lumber a log will yield. The reason there is more than one is that estimating yield means guessing at things that happen later: how thick the saw kerf is, how much slab comes off the outside, how the sawyer bucks and edges. Different people made different guesses, and three of those guesses became standards.

Log rule	Tends to	Where it is common
Doyle	Under-scale small logs	The South and East, most timber sales
Scribner	Land in the middle	The West, government timber
International 1/4	Track actual yield closest	Research, careful buyers

The Doyle, Scribner, and International comparison goes deeper on where each came from, but the short version is below, because the differences are not small.

Doyle, and why small logs look so poor

The Doyle rule is the most widely used in timber sales across the eastern United States, and it is the one that undervalues small logs the hardest. Its formula subtracts four inches from the diameter before squaring, which is a heavy penalty on a thin log.

Work a 12-inch, 16-foot log through Doyle and you get 64 board feet. The same log through International gives about 95. That is not a rounding difference, it is a third of the log vanishing on paper. On a small log the gap is even wider, which is why sellers of small timber hate Doyle and buyers of it do not mind at all.

The practical lesson: on logs under about 16 inches, Doyle reads low, so if you are buying by Doyle you are getting a discount, and if you are selling by it you are giving one.

Scribner and International, for a truer read

The Scribner rule is older and was drawn by diagramming boards inside a circle. It ignores taper and tends to sit between Doyle and International, which is part of why it stuck around for government timber in the West.

The International 1/4-inch rule is the one built to track real yield most closely. It accounts for taper along the log and assumes a 1/4-inch kerf, and study after study has found it comes nearest to what actually comes off the mill. If you want the estimate least likely to embarrass you, International is the rule to scale by, even if the people you trade with quote Doyle.

A fair habit is to scale a log both ways. Read it in Doyle because that is what the sale uses, and read it in International because that is closer to what you will really cut. The distance between the two numbers tells you how much the rule alone is shaping the price.

From log scale to lumber you can sell

Log scale is an estimate of yield, not a promise. Real output swings with saw kerf, log quality, and how carefully the sawyer works. A clean, straight log can beat its International scale, while a log with sweep, rot, or big knots will fall short of any rule.

Once the boards are cut and stacked, you are back to ordinary board-foot math, thickness times width times length in the board foot formula. It helps to know that going in, because a log scaled at 200 board feet by Doyle might saw out to 260 of actual lumber, and knowing that spread is the difference between a fair offer and a bad one. When you are ready to price the sawn lumber, the current lumber prices give you a starting point by species.

Scale before you cut

The whole point of scaling is to know the number before you commit. Measure the small end inside the bark, round the length down to the even foot, and run it through a rule, or better, run it through two. Read Doyle for the deal on the table and International for the truth of the log.

Do that on every log and the guessing stops. Drop your two measurements into the log scale calculator, compare the rules side by side, and you will know what a log is worth before the first board falls away.