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Section 620, Log Scaling

Internal Revenue Manual
Specialized Industry Guidelines - Timber
Section 620, Log Scaling
Last amended: 6-26-1978

Log Scaling

(1) A log rule is a table showing the estimated net lumber yield in board feet for logs of different diameters and lengths. There are many log rules in use--for example, Scribner Decimal C, Spaulding, Humboldt, Columbia River, Doyle, International, and others. These rules are based on mathematical formulas or on diagrams. The diagrams are circles drawn to show the number of one inch boards that can be sawn from logs of different sizes, after compensating for saw kerf (sawdust waste) and slabs. These log rule measurements give the estimated contents of logs in board feet log scale. The log scale is always an estimate. The actual amount of lumber recovered from a log by sawing is determined by measuring the lumber. This measurement is called lumber tally or green chain tally. A board foot is a piece of lumber 1-inch thick by 12 inches square.

(2) The actual log scaling is done with a "scale stick." It is a stick, similar in appearance to a yard stick, with inches and the log rule stamped on it. The scaler measures the diameter of the log at the small end inside the bark (except as noted below), notes the length of the log, finds on the stick the scale for a log of those dimensions and records the scale on a scale sheet.

(3) The scale of a given log may vary considerably according to the log rule used. For example, a log 16 feet long and 14 inches in diameter when scaled with the Doyle rule is shown to contain 100 board feet. The same log, when scaled with the Scribner rule contains 123 board feet, and with the International 1/4" rule 136 board feet.

(4) If a taxpayer's depletion account was based on the Doyle rule and he/she sold logs to a sawmill that used the International 1/4" rule, it is obvious that his/her depletion deduction would be overstated if he/she used the sawmill's scale without converting it to Doyle.

(5) The picture is further complicated by variations in scaling practice. For example, when the Doyle log rule is used, the general practice in the southeast is to measure the diameter inside one bark. The scalers call it "give and take a bark." It is also customary to ignore all but the most flagrant defects. But when Scribner or International rules are used--most often by the U.S. Forest Service in its estimates of timber sales volumes--log diameters are strictly inside bark measurements and defects are carefully compensated for. The result is that the Doyle scale as actually applied will often approximate the Scribner estimate. Certainly the difference would be much less than indicated by the foregoing example.

(6) The logs are scaled in the woods, at scaling platforms, at the pond, in the pond, or on the mill deck. Diameters and lengths are recorded and deductions are usually made for defects. Pulp logs are frequently measured by weighing or they are measured in cords or sometimes by cunits (100 cubic feet). In the East, all logs may be scaled by weighing.

(7) Logs are sawed in the sawmill and the lumber is tallied by actual measurements. The log scale measurements are then corrected to lumber tally by adding the mill overrun or deducting the mill underrun. The resulting cost of production from the saws is expressed in board feet.

(8) The overrun or underrun at the sawmill should be checked. If the green chain tally at the mill (lumber scale) is less than the log scale, the taxpayer has experienced an underrun. This is unusual and could indicate that the log scale is in error. Under IRC 631(a) increasing the log scale normally results in an increase of IRC 1231 gain and a reduction of ordinary income.

(9) In most parts of the country, improved utilization and machinery have increased the overrun of lumber tally to log scale. Recognition of this by the industry has brought changes in scaling methods. In the meantime, the examiner should continue to check differences between log scale and lumber tally to determine if any tax advantage is being gained by use of an incorrect log scale.