The board foot formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
If you measure length in inches, divide by 144 instead of 12. For example, a board 1 inch thick, 6 inches wide and 10 feet long is 1 × 6 × 10 ÷ 12 = 5 board feet.
Quick reference
| Board size | Board feet per linear foot |
|---|
| 1 × 4 | 0.33 |
| 1 × 6 | 0.5 |
| 1 × 12 | 1 |
| 2 × 4 | 0.67 |
| 2 × 6 | 1 |
| 2 × 10 | 1.67 |
| 4 × 4 | 1.33 |
Board feet vs linear feet
Construction lumber like 2×4s is usually sold by the piece or by the linear foot (length only). Hardwoods such as oak, maple and walnut are sold by the board foot because boards come in random widths. Board feet let a lumberyard price wide and narrow boards fairly by their volume.
Tips for buying hardwood
- Make a cut list first, then group parts by thickness.
- Buy 15–30% extra for knots, checks at the ends and grain matching.
- Remember that surfacing (planing) removes thickness, so rough 4/4 stock planes down to about 13/16 inch.
Building a slab or post footing too? Try the concrete calculator.
Last reviewed October 2026.
Frequently asked questions
What is a board foot?
A board foot is a volume of wood equal to a board 1 inch thick, 12 inches wide and 12 inches long, which is 144 cubic inches. Hardwood lumber in the US is usually priced per board foot.
How do I calculate board feet?
Multiply thickness (inches) × width (inches) × length (feet), then divide by 12. A 2 × 6 board 8 feet long is 2 × 6 × 8 ÷ 12 = 8 board feet.
Should I use nominal or actual size?
Rough-sawn hardwood is sold by nominal thickness, measured in quarters: 4/4 is 1 inch, 5/4 is 1.25, 8/4 is 2 inches. Lumberyards usually calculate board feet from that nominal size, even though planed boards are thinner. Ask your supplier which they use.
What does 4/4 or 8/4 mean?
It is the "quarter" system for hardwood thickness. 4/4 (four-quarter) means 4 quarters of an inch, or 1 inch thick. 6/4 is 1.5 inches and 8/4 is 2 inches, in the rough-sawn state.
How much extra lumber should I buy?
Plan for 15–30% extra to allow for defects, knots, cutting waste and grain matching. Projects with many small parts or figured wood usually need more.