A board foot is how lumber is measured and priced — a volume, not a length. Once you know the one formula, you can total a whole cut list and price it. Here is the formula, the nominal-vs-actual trap, and the linear-to-board-feet conversion.
The formula
A board foot is a piece 1 in thick × 12 in wide × 1 ft long (144 cubic inches). Board feet = (thickness in × width in × length ft) ÷ 12. An 8 ft 2×4 is (2 × 4 × 8) ÷ 12 = 5.33 board feet.
Lumber Calculator
Add each size, length and quantity for the board feet, linear feet and cost across your whole list.
Nominal or actual size?
For dressed softwood (framing lumber), board feet use the nominal size — a 2×4 counts as 2 in by 4 in even though it is actually 1½ × 3½ in, because that is how it is sold. For rough-sawn or hardwood lumber priced by the board foot, use the actualmeasured thickness and width. The calculator’s presets are nominal; switch to custom for rough stock.
Linear feet to board feet
Board feet = linear feet × (nominal thickness in × nominal width in ÷ 12). So 100 linear feet of 2×6 is 100 × (12 ÷ 12) = 100 board feet; the same 100 ft of 2×4 is 100 × (8 ÷ 12) = 67 board feet.
Board feet in common sizes
| Size | Board feet per linear foot |
|---|---|
| 2×4 | 0.667 (an 8 ft = 5.33) |
| 2×6 | 1.0 (an 8 ft = 8) |
| 4×4 | 1.333 (an 8 ft = 10.67) |
Cost per board foot
It varies widely by species and grade — construction softwood is often a few dollars per board foot, while hardwoods run much higher. Note that dimensional studs are frequently priced per piece rather than per board foot, so compare like with like before you order.