One hundred 2x4s 8 feet long are 533 board feet: each is 2 × 4 × 8 ÷ 12 = 5.33 bf. Kiln-dried Douglas fir, they weigh about 980 lb, and laid side by side they cover 233 square feet. The calculator above turns any order of lumber into board feet, pieces, coverage and weight — or works back from the board feet or the area you need to the number of pieces.
How the calculator works
Pick a nominal size and a stock length, then count by pieces, by board feet or by the area to cover. The result is the board feet, the number of pieces, the dressed size and volume, the coverage, the weight for the species group, and the cost if you enter a price per board foot or per piece. The table under the drawing shows the common sizes at the length you picked.
Board feet
A board foot is 144 cubic inches — a board 1 in thick, 12 in wide and 12 in long. Lumber is measured on its nominal size, so a piece has thickness × width × length ÷ 12 board feet, with the first two in inches and the length in feet.
| Size | 8 ft | 12 ft | 16 ft |
|---|---|---|---|
| 1x6 | 4.00 | 6.00 | 8.00 |
| 2x4 | 5.33 | 8.00 | 10.67 |
| 2x6 | 8.00 | 12.00 | 16.00 |
| 2x10 | 13.33 | 20.00 | 26.67 |
| 4x4 | 10.67 | 16.00 | 21.33 |
Nominal and dressed sizes
Softwood lumber is planed after drying, so it is smaller than its name. The American Softwood Lumber Standard (PS 20) sets the dressed sizes: 1 in becomes ¾ in, 2 in becomes 1½, 4 becomes 3½, 6 becomes 5½, 8 becomes 7¼, 10 becomes 9¼ and 12 becomes 11¼. Board feet and prices stay on the nominal size; coverage and weight follow the real wood.
Counting by area
For decking, siding or paneling, each board covers its dressed width plus the gap, times its length. 200 ft² of 1x6 boards 12 ft long with ⅛ in gaps takes 36 boards. Counting by the nominal 6 in would give 34 and leave the deck short.
Weight
Weight is the dressed volume times the density at 12 % moisture, from the specific gravity in the USDA Wood Handbook: Douglas fir 0.48, hem-fir 0.45, southern pine 0.51, spruce-pine-fir 0.35. A kiln-dried 2x4 8 ft long weighs about 9.8 lb in Douglas fir and 7.1 lb in spruce. Green and pressure-treated lumber is much heavier until it dries.
Common mistakes
- Board feet from actual sizes. A 2x4 is priced as 2 × 4, not 1½ × 3½ — the difference is 34 %.
- Length in inches. In T × W × L ÷ 12 the length is in feet; with inches divide by 144.
- Coverage by nominal width. Use the dressed width and add the gap.
For joist and rafter sizes, use the Joist Span Calculator and the Rafter Span Calculator.