How to use the Board Foot
- Enter thickness in inches or quarters (4/4, 8/4).
- Enter width in inches and length in inches or feet.
- Enter the number of pieces.
- Read total board feet and cost at your price per board foot.
How the calculation works
Board feet = thickness × width × length in inches ÷ 144, or thickness × width ÷ 12 when length is in feet. One board foot is a piece 1 inch thick, 12 inches wide and 1 foot long. Hardwood thickness is quoted in quarter-inches: 4/4 is one inch, 6/4 is one and a half, 8/4 is two. Rough lumber is measured at its nominal thickness before surfacing, so a 4/4 board that arrives surfaced at 13/16 inch is still sold and billed as a full inch.
Softwood construction lumber is sold by nominal dimension instead — a 2×4 actually measures 1.5 × 3.5 inches after planing — so board-foot maths on framing lumber uses the nominal figures even though the actual section is smaller. For hardwood buying, allow 20–30% over your finished requirement: defects, snipe, jointing and squaring all consume material, and figured or wide boards yield less usable stock than the raw volume suggests. When boards are of irregular width, measure each at its narrowest point, which is how most mills bill.
Board feet = (thickness in × width in × length in) / 144 ; or (T × W × L ft) / 12Source: NHLA board-foot measurement convention: 144 cubic inches, nominal thickness for rough lumber.
Worked example
Six pieces of 8/4 walnut, 7 inches wide and 8 feet long, at 12.50 per board foot.
- Thickness = 2 inches; length = 96 inches.
- Per piece = 2 × 7 × 96 / 144 = 9.33 bd ft.
- Total = 9.33 × 6 = 56.0 bd ft.
- Cost = 56.0 × 12.50 = 700.
56 board feet costing 700 — budget nearer 70 board feet to allow for waste.
Frequently asked questions
What is a board foot?+
144 cubic inches of lumber — a piece 1 inch thick, 12 inches wide and 1 foot long.
Do I use nominal or actual thickness?+
Nominal for rough hardwood and for softwood framing; mills bill on the nominal figure.
What does 8/4 mean?+
Eight quarter-inches, so two inches of nominal thickness.
How much extra should I buy?+
20–30% above finished requirement to cover defects, squaring and milling losses.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.