Board feet are a lumber-volume unit: one foot long, one foot wide, and one inch thick. Suppliers may price rough or surfaced stock differently, so the dimensions behind the number matter as much as the total.
The definition
One board foot is 1 in × 12 in × 12 in. The common formula thickness (in) × width (in) × length (ft) ÷ 12 produces that volume for one board; multiply by quantity for an order.
Metric inputs are converted for comparison. Keep the original metric dimensions in your notes because a supplier may quote actual millimetres rather than a converted board-foot figure.
Nominal and actual sizes
A board sold by a nominal size may be surfaced to a smaller actual thickness and width. Ask the supplier which dimensions drive the quote. Mixing nominal width with actual thickness makes an otherwise tidy calculation misleading.
Board feet are not a structural rating
The unit measures volume only. Species, grade, defects, moisture, span, connections, and design loads determine whether lumber is suitable for a structural use. Use the calculator to compare quantities, not to approve a beam or rafter.
Allow for selection and cutting
Add a separate waste allowance for defects, grain direction, matching, and cutoffs. Expensive hardwood selection and rough-sawn stock may need a different practical allowance than uniform framing lumber.
Worked examples
Ten 2 × 6 × 8 ft boards
- One board: 2 × 6 × 8 ÷ 12 = 8 board feet.
- Multiply 8 by 10 boards.
- Apply any cutting allowance after the base total.
Result: The base order is 80 board feet.
Metric hardwood boards
- Enter 50 × 150 × 2,400 mm and quantity 4.
- Let the calculator convert dimensions to inches and feet.
- Compare the converted total with the supplier’s rough/surfaced description.
Result: The conversion helps compare quotes, but supplier rounding and actual dimensions still control the purchase.