Board Foot Calculator

A board foot is the standard unit for measuring and pricing lumber in North America. One board foot is a piece of wood 1 inch thick, 12 inches wide and 12 inches long, or any other shape holding the same 144 cubic inches.

The formula is: Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12

If your length is in inches rather than feet, divide by 144 instead. That is the only difference between the two versions, and it catches people out constantly. Thickness and width are always in inches; only the length changes units.

Lumber is rarely sold by the piece at a fixed price. Hardwood in particular is priced per board foot precisely because it comes in random widths and lengths, so the yard needs a unit that prices volume rather than count. Cherry at $8 a board foot means the board footage of your cut list is your budget.

Thickness is quoted in quarters of an inch, and read aloud that way: 4/4 is “four quarter” and means 1 inch, 5/4 is 1.25", 6/4 is 1.5", 8/4 is 2", 12/4 is 3". Always calculate board feet on the rough thickness, not the surfaced dimension after planing. A 4/4 board planes down to about 13/16", but you pay for the full inch, because the yard sold you the wood before the planer took its share.

Example: a board 8/4 (2 inches thick), 6 inches wide and 8 feet long: BF = (2 × 6 × 8) ÷ 12 = 96 ÷ 12 = 8 board feet.

A trap worth knowing. Board footage is volume, so it says nothing about whether the boards are the right shape. Twenty board feet of 4" wide stock will not yield a 10" wide tabletop panel without glue-ups, and no amount of extra board footage fixes that. Check your widest single part against the widths on offer before you order.

Planning tip: add 20 to 30% to your calculated footage for defects, grain matching, saw kerf and mistakes. That is the waste factor, and the honest reason for it is that a board with a knot in the wrong place is not a board you can use. Go toward 30% on figured or narrow stock, where you reject more of what you buy.