Log Weight Calculator

A log is modeled here as a cylinder, so volume is pi times the radius squared times the length, and weight is that volume times the species density in pounds per cubic foot. Density is the variable that swings the answer most, because it depends on both species and moisture state. Freshly felled red oak runs about 64 pounds per cubic foot green against roughly 44 pounds once dried, and white pine falls from about 46 to 25. Green hardwoods commonly carry 60 to 100 percent moisture on an oven-dry basis and some softwood sapwood exceeds 150 percent, so a green log can weigh close to twice its seasoned weight. The board foot figures come from log rules, which estimate sawn lumber yield rather than solid volume. The Doyle rule, computed as the small end diameter minus 4, squared, times length divided by 16, subtracts a fixed 4 inch slab allowance and therefore penalizes small logs heavily, while Scribner is a diagram rule and the International quarter inch rule is the most accurate across sizes. The main limitation of the cylinder model is taper: real logs narrow toward the top, so using the large end diameter overstates volume. Foresters instead use Smalian, which averages the two end areas, or Huber, which uses the midpoint area. Bark, typically 10 to 15 percent of gross volume, is included in a cylinder estimate but is not merchantable.

Log rules were commercial instruments before they were forestry science. The Doyle rule is attributed to Edward Doyle and dates to roughly 1825. Its 4 inch deduction and division by 16 were chosen for mental arithmetic in the field rather than for accuracy, and its bias against small logs made it popular with mills and contentious with landowners. J. M. Scribner published his diagram based rule in 1846, drawing circles of boards inside a log cross section to count recoverable lumber. Judson F. Clark developed the International rule in 1906 with an explicit taper allowance and a stated saw kerf, and it became the reference scale for the US Forest Service. Weight scaling largely displaced stick scaling in commercial practice during the middle of the twentieth century, first for pulpwood and later for sawlogs, especially in the US South, because truck scales are fast, objective and immune to disputes over a scaler's judgment. That shift made species density tables operationally important. The USDA Forest Products Laboratory, founded in Madison, Wisconsin in 1910, published the first edition of its Wood Handbook in 1935 and has maintained the green and oven-dry specific gravity tables that most log weight estimates still rely on. ASTM D2395 later codified the laboratory methods for determining wood density and specific gravity.