How many board feet is that?

Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2 × 6 that is 8 feet long is (2 × 6 × 8) ÷ 12 = 8 board feet. If all three dimensions are in inches, divide by 144 instead.

Nominal, for softwood construction lumber. A 2 × 4 is priced as 2 × 4 even though it measures 1½ × 3½ dressed. Rough-sawn hardwood is different: it is measured at its actual rough dimensions, and thickness is quoted in quarters — 4/4 is one inch, 8/4 is two.

A linear foot is just length, so it only means something once you also know the profile. A board foot is a volume, which is why lumber of different sizes can be priced on one consistent unit. Trim and moulding are usually sold by the linear foot; hardwood and rough stock by the board foot.

Because the board-foot price is for the material only. Milling, planing, ripping to width, delivery and short-length surcharges are separate, and hardwood is often sold in random widths and lengths, so a cut list of specific sizes costs more per board foot than the same volume of random stock.