Lumber is sold two different ways, and confusing them leads to ordering the wrong amount or misreading a price. One measures length only, the other measures volume. Knowing which a supplier means saves both money and a return trip.
Linear feet
Linear feet measure length and nothing else. The width and thickness do not enter into it. Trim, moulding, fencing and dimensional lumber bought by the piece are usually counted in linear feet. If you need 40 feet of baseboard, that is 40 linear feet whether the board is narrow or wide. Buying by linear foot is about counting how much length of a particular profile you need.
Board feet
A board foot is a measure of volume. One board foot is a piece 1 inch thick, 12 inches wide and 1 foot long, which works out to 144 cubic inches. Rough sawn lumber and hardwoods are usually priced per board foot, because the price reflects the actual quantity of wood, not just the length.
Worked examples
A 2 by 6 board that is 8 feet long: 2 times 6 times 8 divided by 12 is 8 board feet. A 1 by 4 board 10 feet long: 1 times 4 times 10 divided by 12 is about 3.33 board feet. If you need ten of those 2 by 6 boards, that is 80 board feet in total.
Quick reference
| Board | Per 8 ft length | Per 12 ft length |
|---|---|---|
| 1 x 4 | 2.67 bf | 4 bf |
| 1 x 6 | 4 bf | 6 bf |
| 2 x 4 | 5.33 bf | 8 bf |
| 2 x 6 | 8 bf | 12 bf |
| 2 x 8 | 10.67 bf | 16 bf |
Pricing a board foot order
If a hardwood is priced at a rate per board foot, multiply the rate by your total board feet. Eighty board feet of a wood priced at a given rate is simply eighty times that rate. This is why mills quote per board foot: a long thin board and a short wide board can hold the same volume of wood and cost the same.
Nominal vs actual size
Softwood lumber is sold by nominal size, the size before it was dressed and dried. A 2 by 4 actually measures about 1.5 by 3.5 inches. Board foot pricing uses the nominal size by convention, so use nominal dimensions when matching a per board foot quote. For a precise volume on a finished project, use the actual dressed dimensions instead.
Which one do I need
If you are buying trim or counting a fence run, work in linear feet. If you are pricing rough lumber or a hardwood order from a mill, work in board feet. When in doubt, ask the supplier which unit their price is quoted in before you calculate.