Log Board Feet Calculator

A log board foot calculator estimates the board feet of lumber a log should produce. It is not a measure of the wood in the log. It is an agreed convention used to buy and sell logs, so the number depends on which log rule you use. The three rules in current use in the United States are Doyle, Scribner and International 1/4 inch, and this calculator runs all of them from the same two measurements, the diameter of the small end inside the bark and the log length.

Enter the diameter in inches, or centimetres in metric mode, the length in feet or metres and the number of logs. Pick the rule you want as the headline result. The calculator shows the board feet per log, the total for the load, the total in MBF (thousand board feet) and the value at the price per MBF that you enter. The price box starts with a placeholder, not a market quote.

The default 16 inch, 16 foot log is 144 board feet by Doyle, 166.2 by Scribner and 180.6 by International. That spread is the main thing to understand, and the rest of this page explains where it comes from.

Measure the diameter of the small end of the log, inside the bark, in inches. Measure the length in feet. Then apply the rule. For Doyle, subtract 4 from the diameter, square the result and multiply by the length divided by 16. A 12 inch log that is 16 feet long is 8 squared = 64 board feet. For Scribner, use 0.79 times the diameter squared, minus 2 times the diameter, minus 4, then multiply by the length divided by 16.

The International 1/4 inch rule works on each 4 foot section. A section holds 0.199 D squared minus 0.642 D board feet, and every further section is taken at a diameter half an inch larger, because logs taper. A 16 foot log is four sections, so the diameters are D, D + 0.5, D + 1 and D + 1.5. Add the sections together. Purdue Extension publishes these formulas, and they are the ones used here.

To scale a standing tree, estimate the sawlog length and the small-end diameter of each log in the stem, scale each log, and add the results. If a log has a defect, subtract the board feet that are lost to it from the gross scale.

Doyle is the most widely used rule on private timber in the east and south. It subtracts a fixed 4 inches of diameter, so it under-reads small logs and reads closer to the truth on large ones. Scribner is a diagram rule, built by drawing boards inside a circle, and its printed Decimal C tables round to 10 board feet. International 1/4 inch allows for the kerf and for taper, and Purdue Extension describes it as probably the most accurate of the current rules.

The table of 16 foot logs shows the gap. At 8 inches Doyle gives only 41 percent of the International figure. At 12 inches it is 66 percent, and at 24 inches 94 percent. Virginia Tech Extension gives a 12 inch log as 95, 80 and 64 board feet by International, Scribner and Doyle, which matches the pattern here after the printed rounding.

None of the rules is wrong. Each is fair when buyer and seller use the same one. The only mistake is to compare a price per MBF quoted on one rule with a price quoted on another.

The small end is the narrow end of the log. Log rules use it because the lumber that can be sawn is limited by the narrowest point. Measure inside the bark, across the narrowest direction or as the average of the narrowest and widest, and round down to the whole inch as a scaler would. Using the big end or the middle overstates the log.

Length matters in a straight line for Doyle and Scribner, which are proportional to length. Doubling the length doubles the board feet. International is slightly more than proportional, because every extra section is taken at a larger diameter. A 14 inch log at 8 feet is 62.5 board feet and at 16 feet it is 135.6, a little more than double.

The length does not have to be a multiple of 4 or 2 feet. For International, the calculator counts a part section in proportion, so a 13.5 foot log has three full sections and 0.875 of the next. Publishers' tables list only set lengths, so this saves you from interpolating by hand.

Logs and lumber are often priced per MBF, one thousand board feet. Divide the total board feet by 1,000 and multiply by the price. At $400 per MBF a board foot costs 40 cents. A load of ten 20 inch, 12 foot logs scales 2,040 board feet by Scribner, which is 2.04 MBF. The price box here starts with a placeholder, so replace it with the price in your quote.

Overrun is the lumber a mill saws beyond the log scale. It equals the lumber tally divided by the log scale, minus 1. Small logs scaled by Doyle commonly overrun because Doyle under-reads them. Purdue Extension notes that experienced mill operators know the overrun to expect for a set of logs, and that it is built into the price they can pay. A seller who knows this will prefer a rule that reads closer to the lumber a mill recovers.

Because the price per MBF and the rule go together, always compare offers on one rule, or convert them with the comparison table above.

A board foot is a unit of volume: 1 foot by 1 foot by 1 inch, which is 144 cubic inches. In lumber you calculate it directly. Thickness in inches times width in inches times length in feet, divided by 12. A 2 by 4 that is 8 feet long is 5.33 board feet by its nominal size and 3.50 by its actual dressed size.

A log is round and tapered, so no direct formula applies. The log rule instead predicts how many board feet will come out of the log after the slabs, kerf and edging are lost, which is much less than the cubic volume of the log. A 16 inch, 16 foot log has about 22.3 cubic feet of wood, equal to 268 board feet, while the Doyle scale is 144.

To calculate board feet for boards you have already cut, use the board foot calculator. It handles nominal and actual sizes, waste and the cost of the lumber. For converting board feet to square feet, divide the thickness in inches into 12.

A log rule is an estimate. The real yield of a log depends on the mill, the sawyer, the lumber thickness, the grade of the log and the way it is sawn. Defects such as rot, shake and sweep must be deducted by hand, and bark thickness must be removed from the measured diameter. The International rule is the best of the three for predicting lumber, but even it is rounded and is based on assumptions of taper and kerf.

The diameter is the biggest source of error. A one-inch mistake on a 12 inch log changes the Doyle scale from 64 to 81 board feet, a change of 27 percent. Measure carefully and agree on the method of measuring with the other party.

For the lumber you cut from your logs, the board foot calculator gives the volume and the cost of boards. To work out how much overrun your mill gets as a percentage, the percentage calculator does the division quickly, and the rafter length calculator shows how much framing lumber a roof will need.