Board Feet Calculator — nominal vs actual
Board feet, linear feet and cost for framing lumber, showing both the nominal size you are billed for and the actual surfaced size you build with.
Board feet are billed on the nominal size, but you build with the actual size. A 2×4 is 1-1/2" × 3-1/2". This shows both, because mixing them up is how orders come out wrong.
| Nominal (what you are billed for) | — |
|---|---|
| Actual (what you build with) | — |
| Board feet, one piece | — |
| Board feet, total | — |
| With waste | — |
| Estimated cost | — |
| Linear feet | — |
The step is at 8. PS 20-20 Table 3, minimum dressed dry: nominal widths under 8 lose 1/2 inch, 8 and over lose 3/4. A 2×6 is 5-1/2", a 2×8 is 7-1/4". The error compounds. Six 1×12 laid edge to edge measure 67-1/2", not the 69" a flat half-inch rule predicts. That is a shelf 1-1/2" short before the first cut.
Yield is not constant across sizes. A 2×4 carries 5.25 square inches of real section against a nominal 8, so 66% of the tally is wood; a 6×6 carries 30.25 against 36, or 84%. Price per board foot only compares within a size. At the same rate the 2×4 costs 28% more per cubic inch of actual wood.
Green and rough-sawn are separate columns. S-GRN is dressed oversize on purpose: a green 2×12 leaves the mill at 11-1/2", set from fiber saturation down to 19% moisture on a 2.80% width shrinkage factor (§6.2.5, footnote 5). Rough-sawn follows neither column. §4.2 tallies nonstandard sizes at the rough or nominal size used in manufacture, so a true 2×6 is billed 2×6 and will not sit flush against S4S.
The dry sizes are minimums at the mill, not in your wall. §5.2 measures them at time of manufacture; §6.2.3.1 allows a tolerance below that minimum of 1% per four percentage points of moisture change. Stock dressed at 19% settling to 8% indoors (a rule of thumb) moves eleven points: a 2×12 gives up about 5/16" of width. Those percentages are averages; pieces vary. Lay out to the actual and leave the joint somewhere to go.
One divergence, declared. This page uses the boards-and-dimension column throughout. A timber is nominal 5 inches or more in the least dimension (§3.4.3), and timbers get their own Table 3 schedule: 5 and 6 lose 1/2 inch, 7 through 15 lose 3/4, 16 and over a full inch. The 6×6 in the list agrees at 5-1/2". A custom 8×8 does not. This page reports 7-1/2" × 7-1/4", where PS 20 gives 7-1/4" square dry, 7-1/2" square green.
A board foot is 144 cubic inches of nominal lumber: nominal thickness (in) × nominal width (in) × length (ft) ÷ 12. Softwood is sold this way even though it is surfaced smaller. A nominal 2×4 finishes at 1-1/2" × 3-1/2", a 1× board at 3/4" thick, and nominal widths of 8" and over lose 3/4" rather than 1/2". Those surfaced sizes are the S4S dry dimensions in the American Softwood Lumber Standard; rough-sawn and green stock differ, so measure what the yard actually hands you before cutting a tight fit.
Worked example
Twenty 2×4s, 8 ft long: how many board feet, and what do they actually measure?
- A board foot is nominal thickness × nominal width × length ÷ 12: 2 × 4 × 8 ÷ 12 = 5.33 bf each.
- 20 × 5.33 = 106.7 bf; 160 lineal ft.
- The surfaced size is 1-1/2 × 3-1/2 in — you are billed on the nominal and build with the actual.
106.7 board feet (117 with 10% waste) for 160 lineal feet of 1-1/2 × 3-1/2 stock. At $3.20 a board foot the page prices it.
10 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
How do you calculate board feet?
Nominal thickness × nominal width × length in feet ÷ 12. A 2×4×8 is 5.33 board feet; 20 of them are 106.7.
What is the actual size of a 2×4?
1½ × 3½ inches surfaced. You are billed on the nominal 2 × 4 and build with the actual.
Why are six 1×12 boards not 69 inches wide?
Because a 1×12 is 11-1/4" (PS 20 Table 3: widths of 8 and over lose 3/4 in.), so six measure 67-1/2". A flat half-inch rule predicts 69", and the shelf comes out 1-1/2" short before the first cut.
Does price per board foot compare across sizes?
Only within one size. A 2×4 has 5.25 in² of real section against 8 nominal, 66% wood; a 6×6 has 30.25 against 36, 84%. At the same rate per board foot the 2×4 costs 28% more per cubic inch of actual wood.