Lumber math

Board Foot Formula

Board feet = thickness (in) × width (in) × length (ft) ÷ 12 × quantity.

Use this formula when your thickness and width are in inches and your length is in feet. A board foot measures lumber volume, not surface area: one board foot equals 144 cubic inches.

Open the board foot calculator to total several lumber sizes, switch between imperial and metric units, and estimate cost.

The formula, step by step

1. Multiply the board thickness in inches by its width in inches.
2. Multiply that result by the length in feet.
3. Divide by 12 to convert the result to board feet.
4. Multiply by the number of matching boards.

For a single 2 in × 6 in × 8 ft board: 2 × 6 × 8 ÷ 12 = 8 board feet. For five boards of that same size: 8 × 5 = 40 board feet.

Using nominal or actual dimensions

Use the dimensions your seller uses to price the lumber. Many lumberyards price common construction boards by nominal size, while finished or surfaced hardwood may be sold using actual measured thickness. The formula works either way; changing the dimensions changes the volume result.

Metric dimensions

If your board is measured in millimetres and metres, convert thickness and width to inches and length to feet before using the formula. The calculator handles those unit conversions for each row, so you do not need to convert values manually.

Common questions