Board feet.
Board feet: Calculate board feet for lumber with nominal vs actual dimensions, waste factor, and price total.
Lumber volume in board feet (BF) with optional waste factor and unit pricing. Handles both nominal dimensional lumber (2×4, 2×6) and actual hardwood S4S (rough or surfaced) sizes.
How board feet work
A board foot (BF) is a volume of lumber equal to 144 cubic inches — i.e., 1 inch thick × 12 inches wide × 12 inches long, or any equivalent combination. The formula is:
BF = (thickness × width × length_in_inches) / 144 or equivalently: BF = (thickness × width × length_in_feet) / 12
Nominal vs actual dimensions
Construction-grade softwood lumber is sized by nominal dimensions, but the actual milled size is smaller. A "2×4" is really 1½″ × 3½″ after planing. Board-foot pricing uses the nominal dimensions by convention — even though you're getting less wood than the math suggests. This is a holdover from the days when rough green lumber was actually 2″ × 4″ and shrank during drying and planing.
Hardwood lumber is different: it's priced by actual dimensions, often in quarter-inch thicknesses (4/4, 5/4, 6/4, 8/4, etc.), where "4/4" means 1 inch thick (4 quarters = 1 inch).
Typical waste factors
| Use case | Waste factor | Why |
|---|---|---|
| Framing (straight cuts) | 5–10% | Simple cuts, defects rare in dimensional lumber |
| Decking | 10–15% | End-cuts and minor warping |
| Finish trim / casing | 15–20% | Miters, complex angles, defect culling |
| Cabinetmaking (hardwood) | 20–30% | Grain matching, defects in rough lumber, planing loss |
| Veneer / figured stock | 30–50% | Yield from rough boards is low when matching figure |
| Live-edge slabs | 20–40% | Drying checks, wane, sapwood |
Common pitfalls
- Always specify nominal vs actual. A "100 BF of 1×6 pine" means 100 BF using nominal 1″ × 6″ dimensions (the actual wood is ¾″ × 5½″). A "100 BF of 4/4 walnut" means 100 BF of wood that's actually 1″ thick. These cost very different amounts.
- Hardwood is sold by actual surface measurement. Rough hardwood ("rough sawn") is sold by actual measured dimensions. After surfacing on both sides ("S2S") it's about 1/16″ thinner; surfaced four sides ("S4S") it's ¾″ thick from a 4/4 rough board.
- Lineal feet ≠ board feet. "100 lineal feet of 2×4" is a length measurement. The board-foot equivalent is 100 ft × (2 × 4) / 12 = 66.67 BF.
- Plywood is sold by sheet, not by board foot. A 4×8 sheet of ¾″ plywood has 24 ft² of face area, or roughly 16 BF equivalent, but you'd never buy or price it that way.
- Board feet doesn't include defect culling. The waste factor on this calculator accounts for that. Hardwood specifically is graded (FAS, Selects, #1 Common, #2 Common) by yield — FAS gives ~83% clear face cuttings; #1 Common gives ~67%. If you're buying #1 Common for finish work, your effective yield is much lower than the BF count.
Common questions
What is the actual dimension of a 2x4 piece of lumber?
A nominal 2×4 actually measures 1.5 inches by 3.5 inches after drying and planing. Nominal sizes refer to the rough-sawn dimension before finishing.
How many linear feet are in a square foot of 1x6 siding?
A 1×6 board covers 5.5 inches of width, so each square foot needs about 2.18 linear feet of board (12 ÷ 5.5). Add extra for overlap and waste depending on the siding profile.
How do you calculate board feet for hardwood lumber?
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12, counting any thickness under 1 inch as 1 inch. One board foot equals a 1×12×12-inch volume.
Sources
- Nominal dimensions: American Lumber Standard PS 20 — American Softwood Lumber Standard. Specifies the allowed deviation between nominal and actual dimensions.
- Hardwood sizing: NHLA (National Hardwood Lumber Association) Rules for the Measurement and Inspection of Hardwood and Cypress.
- Plywood sizing: APA — The Engineered Wood Association, Voluntary Product Standard PS 1.
Disclaimer. Board-foot calculations are nominal volumes for pricing and planning. Actual material needed for a project depends on cuts, grain matching, defect culling, and joinery — always order more than the bare math suggests.