How Much Lumber is in a Log?

August 3rd, 2011 by
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cut logForesters use a number of mathematical formulas to estimate the board feet of lumber in a cut log. Using one of these formulas, known as “log rules,” you, too, can estimate the amount of sawn lumber a log will produce. This can be useful, say, if you may want to estimate what you will owe the portable sawmill owner for sawing it up for you (since he probably will charge you per board foot). The estimate will get you close so that the final bill will not be a complete surprise.

A log rule attempts to estimate the number of board feet of lumber in a log. (A board foot in its purest sense is a board 1″ thick, 12″ long and 12″ wide.) It is more difficult than you think, because kerf width will vary from saw blade to saw blade, waste will vary depending upon how the log is sawn, and each species of tree will vary in the amount of taper from the base of the log to the top. Log rules are based on mathematical estimates of the volume of a cylinder with taper adjustment, and a couple are even based on actually drawing board ends in a given size circle equaling the log diameter.

log length measuringMost log rules have been used to calculate the volume of commonly sized logs and printed in table form. You will find one for the International 1/4 Log Rule below. To use any log rule, you will have to take some measurements of the log.

Measure the length of the log and round it down to the nearest even foot. For example, if you have a 15’3″ log, use the 14′ long length in the log rule table. Most loggers will cut logs into lengths only an inch or two greater than the nearest even foot. Remember that the butt of a log usually is not sawn flat, so measure the shorter side of the log for length.

log diameter measuringFinally, measure the diameter at the TOP of the log. Always measure diameter “inside bark” – meaning that you don’t want to capture the bark thickness in your measurement.

Use your measurements with the attached table to determine the approximate number of board feet the log holds. The log in the above photos was 13 inches and 16′, so we estimate the log as having 115 board feet of lumber.

Tim Knight

The board-foot contents of logs according to the International 1/4 Rule
Diameter of log small end, inside bark Length of log (feet)
8 10 12 14 16
Board feet
12 inches 45 55 70 85 95
13 inches 55 70 85 100 115
14 inches 65 80 100 115 135
15 inches 75 95 115 135 160
16 inches 85 110 130 155 180
17 inches 95 125 150 180 205
18 inches 110 140 170 200 230
19 inches 125 155 190 225 260
20 inches 135 175 210 250 290
21 inches 155 195 235 280 320
22 inches 170 215 260 305 355
23 inches 185 235 285 335 390
24 inches 205 255 310 370 425
25 inches 220 280 340 400 460
26 inches 240 305 370 435 500
27 inches 260 330 400 470 540
28 inches 280 365 430 505 585
29 inches 305 385 465 545 630
30 inches 325 410 495 585 675

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