How to Calculate Board Feet: Formula, Units and Lumber Cost
Calculate board feet with inches or feet, work through a 4 BF example, and separate lumber volume from the supplier’s pricing tally.
A board can be eight feet long without containing eight board feet. Length tells you how far the board extends; board feet describe its volume. That distinction matters when you compare two boards with different widths or thicknesses.
The formula and its units
One board foot equals 144 cubic inches: the volume of a piece 1 inch thick, 12 inches wide and 12 inches long. Penn State Extension gives the following formula for sawn lumber. [1]
BF = thickness (in) × width (in) × length (ft) ÷ 12
Keep thickness and width in inches and length in feet for this version. If every measurement is in inches, use the other denominator:
BF = thickness (in) × width (in) × length (in) ÷ 144
The two formulas agree because one foot contains 12 inches. Changing the unit without changing the denominator is an easy way to make an answer twelve times too large or too small.
Worked examples
One board: 1 inch × 6 inches × 8 feet
Write the unit next to each measurement before entering the numbers. The calculation is 1 × 6 × 8 ÷ 12 = 4 BF. As a cross-check, convert 8 feet to 96 inches: 1 × 6 × 96 ÷ 144 also equals 4 BF.
| Thickness × width × length | Quantity | Total BF |
|---|---|---|
| 1 in × 6 in × 8 ft | 1 | 4 |
| 1 in × 6 in × 8 ft | 3 | 12 |
| 1½ in × 8 in × 6 ft | 2 | 12 |
For the last row, one board contains 1.5 × 8 × 6 ÷ 12 = 6 BF. Two identical boards contain 12 BF. When board sizes differ, calculate each row separately and add the results; multiplying one average-looking board by the total quantity can hide a size difference.
From board feet to cost
For a hypothetical quote of $7.50 per BF, a 12 BF tally costs 12 × $7.50 = $90 before any separate tax, delivery or processing charges. This is an arithmetic example, not a current lumber price.
Confirm which dimensions and rounding rules the seller uses for the invoice. Wood-Mizer’s board-foot guide illustrates lumber tallies; a seller’s tally basis and the physical volume of a surfaced board need not use the same inputs. [2] A small measured-volume result is not, by itself, proof that the bill is wrong.
Before you order
- Label thickness, width, length and quantity explicitly.
- Keep each row’s units consistent.
- Confirm the supplier’s tally and price basis before comparing quotes.
- List extra stock for your project separately from the calculated volume. A purchase allowance is a planning choice, not part of the definition of a board foot.
Working from a nominal size such as 2×4? Read nominal versus actual lumber sizes before deciding which dimensions belong in your calculation.
Keep the numbers with your project
WoodShop Toolkit’s board-foot tool keeps multiple boards and lumber costs in one tally. Use the same dimension and pricing basis you agreed with your supplier.
Explore WoodShop Toolkit’s woodworking calculators and real app screens.
Android release is in preparation. Explore the features and screenshots above. iOS: Coming soon.
Sources and scope
- Penn State Extension — Valuing Standing Timber, Board Feet section. Definition and sawn-lumber formula.
- Wood-Mizer — What is a Board Foot?. Lumber tally and pricing context. Examples on this page are our own calculations.
Sources checked October 18, 2026. Calculations and example project records are AppMaven’s own illustrations. They describe the stated assumptions and are not a complete construction plan.