What is a board foot?
A board foot (BF) is the standard unit for buying and selling lumber in the United States and Canada. It is a piece of wood 1 foot long, 1 foot wide and 1 inch thick — 144 cubic inches. Hardwood dealers price almost everything by the board foot, so knowing how to calculate it lets you compare prices and plan a project budget accurately.
How to use the board foot calculator
- Enter the board thickness and width in inches (or switch to mm or cm).
- Enter the length in feet (or inches, metres or centimetres).
- Enter how many boards of that size you need, and add rows for other sizes.
- Optional: add a waste allowance and your price per board foot.
Board foot formula
Board feet = Thickness (in) × Width (in) × Length (ft) ÷ 12 Board feet = Thickness (in) × Width (in) × Length (in) ÷ 144
Use the first version when length is in feet, the second when everything is in inches. In metric, board feet = volume in cubic metres ÷ 0.0023597.
Worked example
You need ten 2 × 4 studs 12 feet long and four 1 × 6 boards 8 feet long, at $8.50 per board foot with 10% waste:
- 2 × 4 × 12 ÷ 12 = 8 BF each → 10 boards = 80 BF
- 1 × 6 × 8 ÷ 12 = 4 BF each → 4 boards = 16 BF
- Total = 96 BF; with 10% waste = 105.6 BF
- Cost = 105.6 × $8.50 = $897.60
Board feet of common lumber sizes
| Nominal size | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 1 × 4 | 2.67 | 3.33 | 4.00 | 5.33 |
| 1 × 6 | 4.00 | 5.00 | 6.00 | 8.00 |
| 2 × 4 | 5.33 | 6.67 | 8.00 | 10.67 |
| 2 × 6 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2 × 8 | 10.67 | 13.33 | 16.00 | 21.33 |
| 4 × 4 | 10.67 | 13.33 | 16.00 | 21.33 |
Nominal vs actual size
A “2 × 4” is not actually 2 inches by 4 inches. After drying and planing it measures about 1.5 × 3.5 inches. Softwood is still sold on the nominal size, so board feet for construction lumber use the nominal numbers. Hardwood is different: it is sold by its rough-sawn thickness in quarters (4/4, 5/4, 8/4) and its actual width and length, often in random widths and lengths. Check how your supplier measures before you compare prices.
Buying tips
- Plan cuts before buying — a cut list shows which board lengths waste the least.
- Surfaced (S2S or S4S) lumber costs more per board foot but saves time and waste.
- Buy a little extra of the same batch so colour and grain match.
Board feet for live-edge slabs and irregular boards
For boards that are not the same width end to end, such as live-edge slabs, measure the width at several points, average them and use the average width. For tapered boards, the average of the two end widths is a good estimate. Thickness should be the thinnest usable point, because that is what you can actually plane the board to.