Board Foot Calculator

A board foot is a unit of volume used almost exclusively for lumber, defined as 144 cubic inches — the volume of a piece one inch thick, twelve inches wide and one foot long. Because it is a volume rather than a length or an area, any board with the same total volume counts the same: a 1 × 12 × 1 ft, a 2 × 6 × 1 ft and a 1 × 6 × 2 ft are all exactly one board foot.

This is what makes it useful for pricing. Hardwood arrives in random widths and lengths rather than standard dimensions, so pricing per piece would be meaningless. Pricing by volume lets a supplier quote one rate for a species and grade regardless of how the individual boards happen to be sized.

A "2×4" has not measured two inches by four inches for a long time. The board is sawn at roughly that size when green, then dried and planed smooth on all four sides, arriving at an actual 1.5 × 3.5 inches. Softwood dimensions each lose half an inch up to 6 inches nominal, and three-quarters of an inch above that — so a nominal 2×10 is actually 1.5 × 9.25 in.

The convention that catches people out is that board footage is calculated and billed on the nominal size. Ten 2×4×8s are sold as 53.3 board feet even though the wood you carry home is closer to 35 board feet of actual volume. This is not a swindle — it is a consistent, universally understood trade convention, and prices are set with it in mind — but it does mean that comparing a board-foot price against a real-volume calculation will always look wrong unless you know which basis is being used.

Hardwood is usually specified in quarter-inches rather than whole inches, written with a slash: 4/4 ("four quarter") is one inch nominal, 8/4 is two inches, 5/4 is an inch and a quarter. The notation exists because hardwood is milled in a wider range of thicknesses than the standard softwood dimensions, and because it is frequently sold rough-sawn, where the nominal and actual thickness are much closer than for surfaced softwood. A 4/4 board bought rough may genuinely measure a full inch; the same board surfaced on two sides (S2S) typically arrives at about 13/16 in.

Framing lumber is used more or less as it comes, so a 10% allowance covers ordinary offcuts. Furniture and cabinet work is different: boards have knots, checks, sapwood and grain that has to be matched across a panel, and a woodworker will reject or cut around a significant fraction of the material bought. A 15% allowance is a minimum for straightforward work, 25–30% is common for anything where appearance matters, and figured or highly-graded stock can run higher still. Buying that margin up front matters more than usual with hardwood, because a second order weeks later may come from a different tree entirely and not match.