A board foot is the unit hardwood lumber is sold in — a volume equal to a 1-inch-thick board, 12 inches wide and 12 inches long (144 cubic inches). The formula is simple, but the traps are real: nominal vs actual dimensions, the rough-lumber "quarter" system, and how board feet differ from the linear feet you buy softwood in. This guide clears all of it.
A board foot is a unit of volume, not length or area. It equals a board one inch thick, twelve inches wide, and twelve inches long — 144 cubic inches of wood. Any combination of dimensions that multiplies to 144 cubic inches is one board foot, so a 1×6 board two feet long is also exactly one board foot.
Using feet for length: 1 × 8 × 10 ÷ 12 = 6.67 board feet. Buy five of them: 6.67 × 5 = 33.3 board feet before waste.
Rough hardwood is specified in quarter-inches of thickness, written as a fraction over four. This is how lumberyards talk, so it pays to know it:
| Quarter | Rough thickness |
|---|---|
| 4/4 | 1 in |
| 5/4 | 1¼ in |
| 6/4 | 1½ in |
| 8/4 | 2 in |
| 12/4 | 3 in |
| 16/4 | 4 in |
Board-foot volume is calculated on this rough (nominal) thickness, even though the board is planed thinner before you take it home.
Lumber is sized twice: the nominal dimension it is named and priced by, and the smaller actual dimension after drying and planing. A 4/4 board is sold as 1 inch but surfaces to about ¾ inch; a softwood 2×4 actually measures 1½ × 3½ inches. For board-foot pricing, use the nominal thickness; for fitting the piece into your project, use the actual size.
You pay for the rough board-foot volume (nominal), but design joinery around the planed actual dimensions. Confusing the two over- or under-estimates both cost and fit.
This distinction decides which calculator you even need. Linear feet measures length only and is how dimensional softwood (studs, framing) is sold — a "10-foot 2×4." Board feet measures volume and is how hardwood and rough lumber are sold. You cannot convert between them without knowing the cross-section, because two boards of the same length hold very different volumes if their thickness and width differ.
Hardwood comes in grades (FAS, Select, #1 Common…) that describe how much clear, defect-free wood each board yields. Lower grades are cheaper but waste more, so the waste factor ties to grade and to how much you must cut around knots and for grain match. Plan 15–20% for most furniture work, more for figure-matched panels.
Hardwood is priced per board foot, varying enormously by species. The total is board feet × price × (1 + waste).
| Species class | Typical figure |
|---|---|
| Poplar / soft maple | $3–$6 / bf |
| Red oak / ash / cherry | $5–$10 / bf |
| Walnut / hard maple | $8–$15 / bf |
| Exotic / figured | $15+ / bf |
Use the board-foot calculator to total a cut list and price it, remembering to enter nominal thickness for accurate volume.