How to Calculate Board Feet
A board foot is a piece of wood 1 in thick, 12 in wide and 12 in long. To calculate board feet, multiply the thickness by the width in inches and the length in feet, then divide by 12. A board 1 in thick, 6 in wide and 8 ft long holds 1 × 6 × 8 ÷ 12 = 4 board feet. Hardwood is sold and priced by the board foot, so this number is what you pay for. To figure board feet for a whole order, work out each board and add them up.
The board foot formula
board feet = thickness (in) × width (in) × length (ft) ÷ 12
or, with every size in inches:
board feet = thickness × width × length ÷ 144
Both give the same answer: 144 cubic inches is one board foot. Multiply by the number of boards for a stack.
Worked examples
| Board | Calculation | Board feet |
|---|---|---|
| 4/4 × 6 in × 8 ft | 1 × 6 × 8 ÷ 12 | 4 |
| 4/4 × 8 in × 10 ft | 1 × 8 × 10 ÷ 12 | 6.67 |
| 5/4 × 6 in × 8 ft | 1.25 × 6 × 8 ÷ 12 | 5 |
| 8/4 × 6 in × 8 ft | 2 × 6 × 8 ÷ 12 | 8 |
| 2×4 × 8 ft | 2 × 4 × 8 ÷ 12 | 5.33 |
| 2×6 × 12 ft | 2 × 6 × 12 ÷ 12 | 12 |
| 4×4 × 8 ft | 4 × 4 × 8 ÷ 12 | 10.67 |
Rough hardwood: thickness in quarters
Hardwood is sold rough, with its thickness in quarters of an inch: 4/4 ("four quarter") is 1 in, 5/4 is 1 1/4 in, 6/4 is 1 1/2 in, 8/4 is 2 in. Board feet are counted at this rough size, even though planing leaves a 4/4 board about 13/16 in thick. Rough boards also come in random widths and lengths, so measure each board, or the average width of a stack, and add them up.
Softwood lumber: nominal sizes
Construction lumber is counted at its nominal size, not its real one. A 2×4 is actually 1 1/2 × 3 1/2 in, but it counts as 2 × 4 in: 0.67 board feet per foot of length.
Board feet, square feet and linear feet
- Board feet to square feet: divide by the thickness in inches. 20 board feet of 1 in lumber covers 20 sq ft; of 2 in lumber, 10 sq ft.
- Linear feet to board feet: multiply the linear feet by the thickness and the width in inches, then divide by 12. 30 linear feet of 1 × 4 is 30 × 1 × 4 ÷ 12 = 10 board feet.
- Cubic metres: one board foot is 0.00236 m³, so one cubic metre is about 424 board feet.
Estimating board feet for a project
Work out the board feet of every part in your cut list, add them up, then add 15–20% for knots, splits and offcuts, more for low grades or if the colour must match. Sheet goods are different: plywood and MDF are bought by the sheet, not the board foot, and a cut list optimizer tells you how many sheets you need.
Our calculator does the sums for a whole list of boards, with the waste and the cost:
Frequently asked questions
What is a board foot?
A volume of wood equal to a board 1 in thick, 12 in wide and 12 in long: 144 cubic inches, or 2.36 litres. Hardwood lumber is priced by the board foot.
What is the formula for board feet?
Thickness (in) × width (in) × length (ft) ÷ 12. With the length in inches, divide by 144 instead.
How do you convert board feet to square feet?
Divide the board feet by the thickness in inches. 10 board feet of 1 in (4/4) lumber covers 10 sq ft; of 2 in (8/4) lumber, 5 sq ft.
How many board feet are in a 2x4?
A 2x4 has 0.67 board feet per foot of length, so a 2x4x8 is 5.33 board feet and a 2x4x10 is 6.67.
What is the meaning of board feet?
Board feet is a unit of volume for lumber: one board foot is 144 cubic inches, a board 1 in × 12 in × 12 in. It measures how much wood there is, not how long a board is.
What is the formula for calculating board feet?
Thickness (in) × width (in) × length (ft) ÷ 12. With every size in inches, divide by 144 instead.