Board Foot Calculator
Work out board feet and cost for hardwood and rough lumber, the way lumberyards price it.
How to use this board foot calculator
Hardwood is sold by the board foot: a piece 1 inch thick, 12 inches wide and 1 foot long (144 cubic inches). Pick the board's thickness in "quarters": 4/4 ("four quarter") means 1 inch, 8/4 means 2 inches. Then enter the width in inches, the length in feet and how many boards.
The extra percentage covers knots, cracks, sapwood and offcuts you can't use. Woodworkers often add 20 to 30% for furniture projects.
Rough vs. finished size
Board feet are measured on the rough size. A rough 4/4 board planes down to about ¾ inch, and an 8/4 board to about 1¾ inches, so plan your cut list on the finished thickness but buy by the rough one. Construction lumber (2×4s, 2×6s) is usually sold by the piece or linear foot instead.
| Rough thickness | Typical finished thickness |
|---|---|
| 4/4 | ¾ in |
| 5/4 | 1 in |
| 6/4 | 1¼ in |
| 8/4 | 1¾ in |
The math behind it
Board feet = thickness (in) × width (in) × length (ft) ÷ 12 × number of boards. Cost = board feet × price per board foot.
Example: three 8/4 boards, 8 inches wide and 10 feet long, are 2 × 8 × 10 ÷ 12 × 3 = 40 board feet. At $8 per board foot, that's $320 (or about 48 board feet and $384 with 20% extra).
Often used together
Quick answers
How many board feet are in a 2×4?
An 8-foot 2×4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet, using its nominal size. Lumberyards use the nominal size for board feet even though the real board is 1½ × 3½ inches.
Why is hardwood sold by the board foot?
Hardwood boards come in random widths and lengths, so pricing by volume is fairer than pricing by the piece.
How much extra wood should I buy?
For furniture, 20 to 30% is typical to work around knots, checks and grain you don't like. For simple shop projects, 10 to 15% is usually enough.