Board Feet Explained: Pricing Hardwood Lumber Without Getting Shortchanged

Hardwood is not sold by the linear foot. It is sold by the board foot — a unit of volume equal to 144 cubic inches, which is a board 12 inches long, 12 inches wide and 1 inch thick. Because the unit is volumetric, a narrow thick plank and a wide thin plank can carry the same board-foot price despite looking nothing alike. Getting this wrong is the most common way buyers overpay at a lumber yard.

All the multiplications below are straightforward; a general-purpose online calculator handles them, but the unit handling is where the errors creep in.

The Formula

Board feet = (thickness in inches × width in inches × length in feet) ÷ 12

Note the mixed units: thickness and width in inches, length in feet. This is the standard industry convention and the source of most calculation mistakes.

Worked Examples

Piece	Thickness	Width	Length	Board feet
Common 1×6	1 in	6 in	8 ft	4.00
2×4 stud	2 in	4 in	8 ft	5.33
2×10 joist	2 in	10 in	16 ft	26.67
4/4 walnut board	1 in	7.5 in	6 ft	3.75
8/4 maple	2 in	6 in	5 ft	5.00

Checking the first row by hand: 1 × 6 × 8 = 48; 48 ÷ 12 = 4 board feet. The 2×10 joist is 2 × 10 × 16 = 320; 320 ÷ 12 = 26.67.

Quarter System: What 4/4 and 8/4 Mean

Hardwood thickness is quoted in quarters of an inch, written as a fraction:

Marking	Rough thickness	Surfaced (S2S) thickness
4/4	1 in	13/16 in
5/4	1¼ in	1-1/16 in
6/4	1½ in	1-5/16 in
8/4	2 in	1-3/4 in
12/4	3 in	2-3/4 in

Prices are quoted on rough thickness — the nominal quarter figure — even after the board has been surfaced. That is intentional: surfacing removes material, and the trade bills on the volume that entered the mill. This is why a surfaced 4/4 board measures 13/16 inch thick but still bills as 1 inch.

Nominal vs Actual: Softwood Is Different

Construction lumber (softwood) uses nominal sizing with a fixed reduction, and board feet is rarely the pricing unit — linear feet or per-piece is.

Nominal	Actual (dressed)
1×4	¾ × 3½ in
2×4	1½ × 3½ in
2×6	1½ × 5½ in
2×10	1½ × 9¼ in

If you compute board feet on a 2×4 using the actual dimensions you get 1.5 × 3.5 × 8 ÷ 12 = 3.5, where the nominal formula gives 5.33. Neither is wrong — they answer different questions. Suppliers bill softwood by the nominal figure, which is why the nominal number is the one that matters commercially.

Practical Buying Tips

Add 15–20% for waste on a furniture project. Board feet priced at the counter is the raw volume, not the usable volume after milling.
Ask whether the price is rough or surfaced — surfaced usually costs more per board foot but yields less waste.
Watch the width rounding rule. Some yards round the width to the nearest whole inch, which can add 5–8% to a narrow board’s bill. Ask before you buy.
Compare against a linear-foot price when the width is standard, so you can see whether the board-foot quote is competitive.

Frequently Asked Questions

Why divide by 12 and not 144? Because length is already in feet. If you keep all three dimensions in inches you would divide the product by 144 to reach the same answer.

How much does a board foot weigh? Roughly 2.5–3.5 pounds for common hardwoods at 8–12% moisture content. Oak runs heavier than poplar at the same volume. If you are estimating a load, multiply total board feet by about 3 pounds and add the pallet weight.

Can I use this for sheet goods? Plywood and MDF are sold by the sheet (4×8 ft = 32 square feet), not by board feet. To compare cost per volume, note that a ¾-inch 4×8 sheet contains 32 × 0.75 ÷ 12 = 2 board feet of thickness-equivalent material per square foot — but the comparison is rarely meaningful because sheet goods and solid lumber are used differently.

If you are pricing a whole project, combine the board-foot total with a coverage estimate so you know whether you bought enough. Our guide to paint coverage math uses the same volume-and-waste logic for finishing materials.