Lumber Calculator
Calculate board feet and total cost for any quantity of lumber from its thickness, width and length.
Free · No sign-up · Runs in your browser · Last reviewed November 2026
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About the Lumber Calculator
A board foot is a volume of wood equal to 1 inch thick, 12 inches wide and 12 inches long. Hardwood is priced by the board foot, while construction lumber is sold per piece. This lumber calculator uses the nominal dimensions you enter to find board feet and total cost.
How to use it
- Enter the board thickness and width in inches and the length in feet.
- Enter the quantity and the price per board foot.
- Press Calculate board feet for the total volume and cost.
Board foot formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12. A 2 × 6 × 8 ft board is 8 board feet. Ten of them are 80 board feet.
Board feet in common lumber
| Size | Length | Board feet |
|---|---|---|
| 2 x 4 | 8 ft | 5.33 |
| 2 x 4 | 10 ft | 6.67 |
| 2 x 6 | 8 ft | 8.00 |
| 2 x 8 | 12 ft | 16.00 |
| 2 x 10 | 12 ft | 20.00 |
| 4 x 4 | 8 ft | 10.67 |
Remember
- Nominal sizes (2 x 4) are larger than actual sizes (1.5 x 3.5 in), but board feet are usually figured on nominal size.
- Add 10% for waste and defects.
- Prices change often, so confirm with the lumberyard.
Board foot examples and lumberyard tips
Hardwood is where board feet matter most. Suppose you are buying twelve 1 × 6 × 8 ft oak boards. Each is 4 board feet, so the order is 48 board feet. Adding 10% for defects and cuts brings it to 52.8. At a hypothetical $6.50 per board foot, that is about $343.20.
Things to watch
- Rough versus surfaced. Hardwood is often sold rough at nominal thickness (such as 4/4, meaning 1 inch), then planed smaller. Buy extra thickness if you need a specific finished dimension.
- Quarter inch thickness codes. 4/4 is 1 inch, 8/4 is 2 inches. Use the actual inch value when entering thickness.
- Short and narrow boards. Many yards measure each board and round it, so your total may differ slightly.
- Moisture. Wood that is too wet will shrink and warp after building; ask about kiln-dried stock.
For framing projects such as a deck, the deck calculator counts boards and joists directly.
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12.
How many board feet in a 2x4x8?
A 2 by 4 by 8 foot board is 5.33 board feet.
Why is lumber sold by the board foot?
It gives a fair price for hardwoods of varying sizes. Construction lumber is generally sold by the piece.
Should I use nominal or actual size?
Lumberyards typically price by nominal size.
How much extra lumber should I buy?
Plan for about 10% extra to cover defects and cuts.
What does 4/4 mean in lumber?
It is a thickness measured in quarters of an inch: 4/4 is 1 inch, 5/4 is 1.25 inches and 8/4 is 2 inches, based on rough, unsurfaced stock.
Do I pay for the full nominal size when boards are planed?
Hardwood yards generally charge by the board foot of the rough size before surfacing, so planing does not reduce the price. Ask the yard how they measure and whether they sell surfaced stock.
Last reviewed: November 2026.