How the calculator works
A board foot is the volume of a 12″ × 12″ × 1″ piece of wood. The formula:
Board feet = (thickness″ × width″ × length′) ÷ 12
Note the mixed units: thickness and width in inches, length in feet. It's the standard unit for hardwood because hardwoods come in random widths and lengths; pricing by volume is the only fair way.
Worked example: an 8/4 walnut board 7″ wide and 9 ft long: (2 × 7 × 9) ÷ 12 = 10.5 board feet. At $12/bd ft, that board costs $126.
The quarter system
Hardwood thickness is quoted in quarters of an inch, measured rough, before surfacing:
- 4/4 ("four-quarter") = 1″ rough → surfaces to ~13/16″
- 5/4 = 1¼″ rough → ~1-1/16″
- 6/4 = 1½″ rough → ~1-5/16″
- 8/4 = 2″ rough → ~1¾″
You pay for the rough dimension even when buying surfaced stock. That's not a scam, it's the milling loss built into the trade.
Buying tips
- Plan projects with 20–30% extra board footage: defects, grain matching, and test cuts consume real wood.
- Random widths mean your 6″-wide part might come from an 8″ board, so figure yield, not just area.
- Construction lumber (2×4s etc.) is sold by the piece, not board feet; this unit matters at hardwood dealers and sawmills.