A board foot is the standard US unit for measuring lumber volume. This converts a board’s nominal dimensions and length into board feet.
How it works
Board feet
board feet = (thickness × width × length, all in inches) ÷ 144
A board foot is defined as 12 × 12 × 1 inches — 144 cubic inches exactly — a definitional unit, not a measured or conventional one.
Nominal size, not actual size
A “2×4” does not actually measure 2 inches by 4 inches — after milling and drying it’s closer to 1½ × 3½ inches. This is the single most common lumber-buying confusion. Board footage is conventionally calculated from the nominal size regardless — that is the industry convention for pricing lumber — which is why this calculator asks for nominal dimensions rather than the smaller actual milled size.
How to use this calculator
- Enter the nominal thickness and width — the numbers printed on the lumber, like “2” and “4” for a 2×4.
- Enter the length in feet.
- Enter how many identical boards you need.
Frequently asked questions
Why use nominal size instead of the actual, smaller milled dimensions?
Because that’s the industry convention lumber is priced and sold by — a board-foot price is quoted against the nominal size, so using actual dimensions here would give a figure that doesn’t match how lumber yards actually charge.
What’s the difference between a board foot and a linear foot?
A linear foot measures only length, ignoring thickness and width entirely. A board foot accounts for all three dimensions, which is why a thick, wide board and a thin, narrow one of the same length are very different numbers of board feet.
Is 144 always the right number to divide by?
Yes — it’s the definition of a board foot (12×12×1 inches), not a conversion factor that varies by lumber type or region.
Does hardwood get measured the same way as softwood?
The board-foot unit itself is the same either way, though hardwood is more commonly sold and priced by the board foot than dimensional softwood framing lumber, which is often priced per linear foot or per piece instead.
Why does the “number of boards” field matter for a project estimate?
Because most real projects need more than one identical board — this multiplies the per-board figure directly, giving a project total rather than requiring the multiplication to be done separately by hand.
