How to use the board foot calculator
- Enter the thickness and width in inches. For rough hardwood, use the nominal thickness: 4/4 is 1 in, 5/4 is 1.25 in, 8/4 is 2 in.
- Enter the length in feet.
- Enter how many boards of that size you are buying.
- Add the price per board foot from the lumberyard to get the total.
Metric users can enter centimetres and metres; the result is still given in board feet, plus volume in cubic metres. Lumber yards usually price hardwood by the board foot, which is why Decoratoradvice reports the total in board feet.
Board foot formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
Or, all in inches: thickness × width × length ÷ 144
A board foot is the volume of a board 1 in thick, 12 in wide and 12 in long: 144 cubic inches.
Worked examples
A 2 × 6 that is 8 ft long:
2 × 6 × 8 ÷ 12 = 8 board feet
Ten boards of 4/4 hardwood, 8 in wide and 10 ft long, at $5.00 per board foot:
1 × 8 × 10 ÷ 12 = 6.67 board feet each
6.67 × 10 = 66.67 board feet
66.67 × $5.00 = $333.33
Nominal and actual sizes
Lumberyards usually work out board feet from the nominal size, not the planed size you can measure. A 2 × 6 is about 1½ × 5½ in once surfaced, but it is counted as 2 × 6. Hardwood is sold on its rough thickness in quarters of an inch, so 4/4 stock is counted as 1 in thick even after planing. Ask your supplier which dimensions their price uses.
| Nominal thickness | Quarter name | Thickness to enter |
|---|---|---|
| 1 in | 4/4 | 1 in |
| 1¼ in | 5/4 | 1.25 in |
| 1½ in | 6/4 | 1.5 in |
| 2 in | 8/4 | 2 in |
When board feet matter
Hardwood, live-edge slabs and some specialty softwoods are priced by the board foot. Most construction lumber at home centres is priced per piece or per linear foot instead, so for framing you will usually count pieces with the stud calculator or the deck calculator.
Tips
- Rough hardwood has knots, checks and offcuts, so buy more than your finished parts need. How much more depends on the grade and your cutting list.
- Width varies on rough boards. Measure the narrowest point if the yard does.
- Keep a separate line for each board size, then add the results.
Common mistakes
- Using inches for length. With the ÷ 12 formula, length must be in feet.
- Mixing nominal and actual sizes between the price list and your measurements.
- Forgetting the quantity. The formula gives board feet for one board.
Frequently asked questions
How many board feet are in a 2 × 4 × 8?
2 × 4 × 8 ÷ 12 = 5.33 board feet, using nominal dimensions.
How do I calculate board feet for a slab?
Measure the average thickness and width in inches and the length in feet, then use the same formula. For uneven slabs, take several width measurements and average them.
What is the difference between a board foot and a linear foot?
A linear foot measures length only. A board foot measures volume, so a wide or thick board has more board feet per linear foot than a narrow one.
How many board feet are in a cubic foot?
- A cubic foot is 1,728 cubic inches, and a board foot is 144 cubic inches.
Does plywood use board feet?
No. Sheet goods are sold by the sheet. Use the plywood calculator for sheet counts.
Can I use this for rafters?
You can total the board feet of rafter stock once you know each rafter's length from the rafter length calculator, though framing lumber is usually bought by the piece.
Key takeaways
- Board feet = thickness (in) × width (in) × length (ft) ÷ 12.
- One board foot is 144 cubic inches; 12 board feet make a cubic foot.
- Prices usually use nominal or rough sizes, not planed sizes.
- Multiply by quantity and price per board foot for the total cost.