How to Calculate Board Feet
Board feet measure lumber by volume, not length. The formula is thickness in inches × width in inches × length in feet ÷ 12, times how many pieces. Here is the formula worked through, the board feet in common boards, and the two things people get wrong.
By the Calculate My Reno Team / Published
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A board foot is a measure of lumber volume - the wood in a piece 1 inch thick, 12 inches wide and 1 foot long, which is 144 cubic inches. Because it is a volume, it counts thickness, width and length together, which is why sawmills and hardwood dealers price by it.
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Enter the thickness, width, length and quantity of each board and the board foot calculator totals the board feet, the volume and the cost at your price per board foot. The rest of this guide is the formula so you can check the number by hand.
The board-foot formula
board feet (one piece) = thickness_in × width_in × length_ft ÷ 12
project total = board feet per piece × quantity, summed over sizes
1 board foot = 144 cubic inches = a 1 in × 12 in × 1 ft piece
The ÷ 12 is what turns inches-and-feet into board feet: thickness × width gives square inches, and dividing the inches-and-feet product by 12 converts it to the 144-cubic-inch board foot. If you measure the length in inches instead of feet, divide by 144 rather than 12.
Worked example
Ten 2×4s at 8 ft, plus four 1×6 shelf boards at 10 ft:
- One 2×4×8: 2 × 4 × 8 ÷ 12 = 64 ÷ 12 = 5.33 board feet.
- Ten of them: 5.33 × 10 = 53.3 board feet.
- One 1×6×10: 1 × 6 × 10 ÷ 12 = 5 board feet; four of them = 20 board feet.
- Project total: 53.3 + 20 = 73.3 board feet (about 6.1 cubic feet, or 0.17 m³).
Board feet in common boards
The board feet in one piece depend only on its size. Multiply by your quantity:
| Nominal size | Length | Board feet (each) |
|---|---|---|
| 1 × 4 | 8 ft | 2.67 |
| 1 × 6 | 8 ft | 4.00 |
| 1 × 8 | 8 ft | 5.33 |
| 2 × 4 | 8 ft | 5.33 |
| 2 × 4 | 10 ft | 6.67 |
| 2 × 6 | 8 ft | 8.00 |
| 2 × 8 | 8 ft | 10.67 |
| 2 × 10 | 10 ft | 16.67 |
| 4 × 4 | 8 ft | 10.67 |
Two things people get wrong
- Nominal, not actual. Use the size the board is sold as. A 2×4 is figured 2 by 4, not its real 1½ × 3½ inches - see nominal vs actual lumber sizes.
- Board feet are not linear feet. A foot of 1×6 is half a board foot; a foot of 1×12 is a whole one. If a board is sold by length you want linear feet instead - the difference is covered in what is a board foot.
Hardwood quarters
Specialty yards sell hardwood rough and quote thickness in quarters of an inch: 4/4 is 1 inch, 5/4 is 1.25, 8/4 is 2. Always figure board feet on the rough quarter thickness, since that is what you are charged for - see what 4/4, 5/4 and 8/4 mean. Enter 4/4 as 1, 5/4 as 1.25 and 8/4 as 2 in the calculator.
Frequently asked questions
How do you calculate board feet?
Multiply the thickness in inches by the width in inches by the length in feet, then divide by 12, and multiply by the number of pieces. A 2×4 that is 8 ft long is 2 × 4 × 8 ÷ 12 = 5.33 board feet, so ten of them are 53.3 board feet. The 12 turns the mixed inches-and-feet into the 144 cubic inches that make one board foot.
What is the board foot formula?
Board feet = (thickness_in × width_in × length_ft ÷ 12) × quantity. If the length is in inches rather than feet, divide by 144 instead of 12, since one board foot is 144 cubic inches. Both give the same answer because 12 × 12 = 144.
How many board feet are in a 2x4?
It depends on the length, because a board foot is a volume. A 2×4 holds 2 × 4 ÷ 12 = 0.667 board feet per foot of length: an 8 ft 2×4 is 5.33 board feet, a 10 ft is 6.67, and a 12 ft is 8. Use the nominal 2 by 4, not the actual 1½ × 3½, when figuring board feet.
Do you use nominal or actual size for board feet?
Nominal - the size the board is sold as. A 2×4 is figured as 2 by 4 even though it measures about 1½ × 3½ inches after planing, and softwood board-foot pricing follows that convention. For rough hardwood quoted in quarters, the quarter thickness (4/4 = 1 in, 8/4 = 2 in) is the nominal figure you use.
How do I figure board feet for a whole project?
Work out the board feet for each size of board on your cut list, then add them up. Keep the sizes separate rather than averaging, because a few wide or thick pieces carry far more volume than a stack of thin ones. Add 10 to 15% for offcuts and defects, especially with rough lumber you cut to size.