Board foot calculator
Board feet from nominal thickness, width, and length. Plus the actual surfaced volume that figure really stands for, and the conversion that lets a per-board-foot hardwood quote go head to head with a per-linear-foot shelf price.
01 How the math works
A board foot is a nominal volume: 144 cubic inches, the amount of wood in a piece 1 ft × 1 ft × 1 in nominal. To get board feet, multiply nominal thickness in inches by nominal width in inches by length in feet, then divide by 12.
Total = board feet per piece × number of pieces
The dimensions in that formula are the nominal ones — the "2×8" stamped on the tag, not the smaller size the board actually is. That is the convention the lumber trade prices on, and it's also where the number stops describing physical wood. The calculator carries both: the nominal board-foot count and the surfaced actual volume from the PS 20 dimensions.
The price line does one more conversion. Hardwood is quoted per board foot; dimensional softwood at the home center is usually priced by the piece or per linear foot. Multiply board feet by the per-board-foot price for a total, then divide by the linear length to get an equivalent price per linear foot you can hold against a shelf tag.
02 Worked example
Take a framing order of 200 linear feet of 2×8 (61 m of 38×184 mm). Board feet come out to 200 × (2 × 8) ÷ 12 = 266.67 bf.
That's the number a supplier bills. The wood itself is smaller: a 2×8 surfaces to 1.5 × 7.25 in (38 × 184 mm), a 10.875 in² section against the nominal 16 in². So the 266.67 board feet stand for about 15.1 ft³ of actual lumber — roughly 68% of the nominal figure. If a hardwood dealer quoted the same run at, say, a per-board-foot price, dividing the total by 200 ft gives the per-linear-foot number to compare against the softwood shelf price.
03 When this calculator is wrong
Board feet describe nominal size, and nominal size is not the wood in your hands. That gap is the whole reason this page exists, and it's where most board-foot calculators go quiet.
- Nominal board feet overstate the physical wood. A 2×8 is 1.5 × 7.25 in surfaced, not 2 × 8. The actual cross-section is 10.875 in² against a nominal 16 in², so the board-foot count is about 32% higher than the real volume (per PS 20). Fine for pricing softwood, which the trade quotes on nominal — wrong if you're estimating actual volume, shipping weight, or a glue-up.
- 5/4 stock is the sharpest trap. Nominal 1-1/4 in decking is milled to 1 in actual — 20% thinner than the thickness the board-foot math uses. A porch floor priced in 5/4 board feet buys 20% less thickness than the number suggests.
- Board feet only line up with a price if that's how the wood is sold. Softwood 2×material at the home center is priced per piece or per linear foot, not per board foot. The board-foot count is a comparison tool there, not the price — use the linear-foot conversion to make the two quotes comparable.
04 What to do with the result
Once the two prices are in the same units, order in the longest stock that fits the run. Buy lumber long and cut it short. The per-linear-foot premium on 16 ft and 20 ft pieces is typically under 15% over 8 ft and 10 ft, and single long pieces beat splicing shorter ones on framing runs over 12 ft — fewer joints, fewer weak points. The exception is transport: a 20 ft 2×12 doesn't fit in most pickups without overhang flags, and the delivery fee can erase the splice savings on a small order.
05 Common questions
- How do you calculate board feet?
- Multiply nominal thickness in inches by nominal width in inches by length in feet, then divide by 12. A 2×8 that's 8 ft long is (2 × 8 × 8) ÷ 12 = 10.67 bf. Multiply by the number of pieces for the order total.
- What is a board foot?
- A board foot is 144 cubic inches of nominal lumber — a piece 1 ft long, 1 ft wide, and 1 in thick, or any shape with the same nominal volume. It's a volume unit, which is why thickness and width both matter, not just length.
- How many board feet are in a 2×4×8?
- (2 × 4 × 8) ÷ 12 = 5.33 bf. Note that's the nominal figure. The board actually measures 1.5 × 3.5 in, so the real wood is about two-thirds of what the board-foot number implies.
- Is a board foot the same as a linear foot?
- No. A linear foot measures length only; a board foot measures volume. A 1×12 and a 1×6 of the same length have the same linear footage but the 1×12 has twice the board feet. To compare a per-board-foot price with a per-linear-foot price, multiply board feet by the board-foot price and divide by the total length.
- Why is hardwood sold by the board foot but softwood by the piece?
- Hardwood ships in random widths and lengths, so a per-piece price would be meaningless — board feet normalize odd sizes to one volume figure. Hardwood thickness is quoted in quarters: 4/4 is 1 in nominal, 5/4 is 1-1/4 in, 8/4 is 2 in. Softwood comes in fixed nominal sizes, so the yard can price it per piece or per foot.