How to Calculate Board Feet (and the Lumber Cost)

Hardwood, and lumber at many yards, is priced by the board foot: a piece 1 inch thick, 12 inches wide and 1 foot long, which is 144 cubic inches. To order wood or compare prices, you turn each board into board feet.

For learning and planning practice. Check your local building codes and the manufacturer’s numbers before you build: the code numbers here are typical values, not the law where you live.

Try it with your own problem ↓

The steps

Read the thickness and width in inches and the length in feet. For dimension lumber (2×4, 2×10) use the nominal size, the name it is sold by.
Multiply: thickness × width × length.
Divide by 12. (If the length is in inches, divide by 144 instead.)
Multiply by the number of boards, if there are several.
For the cost, multiply the board feet by the price per board foot, and round the money at the end.

A worked example

How many board feet are in a 2×10 that is 16 ft long, and what does it cost at $1.25 per board foot?

Thickness 2 in, width 10 in, length 16 ft.
Multiply: 2 × 10 × 16 = 320.
Divide by 12: 320 ÷ 12 = 26 2/3, about 26.67 board feet.
Cost: 26 2/3 × $1.25 = $33.333…, which rounds to $33.33.
Check in inches: 2 × 10 × 192 = 3,840 cubic inches, and 3,840 ÷ 144 = 26 2/3. ✓

The board is 26 2/3 board feet (about 26.67) and costs $33.33.

Why it works

A board foot is a fixed amount of wood, 144 cubic inches, the same way a gallon is a fixed amount of milk. Multiplying the three sizes gives the volume, and dividing by the size of one board foot counts how many fit. With the length in feet, each foot already holds 12 of the inches, so the 144 shrinks to 12.

Try it with your own problem

Open The Framing Square (free) with this example already filled in. It shows every step, and you can type over it with your own numbers.

Work it out: a 2×10, 16 ft long, at $1.25 per board footOpens The Framing Square with this example

Or try these

More carpentry math, every step written out: open The Framing Square.

Common mistakes

Mixing feet and inches. With the length in feet, divide by 12; with the length in inches, divide by 144.
Using the actual size. A 2×10 really measures 1 1/2" × 9 1/4", but yards count board feet from the nominal 2 × 10.
Misreading hardwood thickness. Hardwood is sold in quarters of an inch: 4/4 is 1 inch, 8/4 is 2 inches.
Rounding each board. Add the exact board feet, then round the total or the money once.

Questions people ask

How many board feet are in a 12 ft 2×6?

2 × 6 × 12 ÷ 12 = 12 board feet.

What does 8/4 lumber mean?

Eight quarters of an inch, so 2 inches thick (rough). An 8/4 board 6 in wide and 8 ft long is 2 × 6 × 8 ÷ 12 = 8 board feet.

Why divide by 12?

A board foot is 1 in × 12 in × 1 ft. With the length already in feet, each board foot needs 12 square inches of end: thickness × width ÷ 12.

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