Lumber measurement guide
Board feet vs linear feet vs square feet
A six-foot board can measure six linear feet, four square feet and four board feet at the same time. Those answers describe different properties of the same piece of wood. Before comparing a quote or entering a shopping list, identify whether you need length, area or volume.
This guide uses an illustrative board measured at 1 inch thick, 8 inches wide and 6 feet long. The numbers are entered dimensions, rather than a promise about what a product with a nominal size label will measure.
Linear feet measure length
A linear foot is one foot of length. Our example board is 6 linear feet long. Its thickness and width do not change that result. Three pieces of the same length provide 18 linear feet, even if one is wider than another.
Linear feet help compare pieces when their cross-sections are already specified. A price per linear foot only makes sense alongside the relevant product size: six linear feet of a narrow strip and six linear feet of a wide plank contain different amounts of wood. If a quote says only “per foot,” ask which unit the supplier means.
Square feet measure area
For a rectangular board's broad face, square feet equal width in feet multiplied by length in feet. Convert our 8-inch width to feet first: 8 ÷ 12 = 2/3 foot. Then multiply by 6 feet to get 4 square feet.
This is the area of one broad face. It is not the area of every surface of the board. A covering or finishing estimate may need a different calculation because joints, gaps, overlaps, edges or both faces can matter. Likewise, four square feet of board face does not guarantee four square feet of usable finished project parts.
Board feet measure volume
A board foot is 144 cubic inches: the volume of a piece 1 inch thick, 12 inches wide and 12 inches long. For thickness and width in inches and length in feet, calculate thickness × width × length ÷ 12. If all three dimensions are in inches, divide by 144 instead. Wood-Mizer explains the board-foot unit and its mixed-unit formula.
Our example is 1 × 8 × 6 ÷ 12 = 4 board feet. Using a length of 72 inches gives the same answer: 1 × 8 × 72 ÷ 144 = 4. For three identical boards, multiply by the quantity after calculating one board: 4 × 3 = 12 board feet.
Why the numbers sometimes match
Our example's square-foot and board-foot totals both equal four because the thickness is exactly one inch. That equality disappears when thickness changes. Keep width and length the same, but use a 2-inch thickness: face area stays at four square feet while volume becomes eight board feet.
| Dimensions | Linear feet | Face square feet | Board feet |
|---|---|---|---|
| 1 in × 8 in × 6 ft | 6 | 4 | 4 |
| 2 in × 8 in × 6 ft | 6 | 4 | 8 |
| 1 in × 4 in × 6 ft | 6 | 2 | 2 |
Choose the measurement before comparing costs
You cannot convert a linear-foot total to board feet without knowing thickness and width. You cannot convert face square feet to board feet without thickness. When those dimensions vary across your shopping list, calculate each row separately, then add the volumes.
For an illustrative rate of $7 per board foot, our 4-BF board has a base estimate of $28. At an illustrative $5 per linear foot, the same six-foot board costs $30. These are invented rates for demonstrating arithmetic, not current lumber prices. Taxes, milling, delivery and a vendor's tally basis can change the final quote.
Use the calculator for the volume of your entered sizes and an optional price estimate. Before using measurements from a surfaced board for a purchase estimate, read how rough and surfaced dimensions differ. The unit tells you what is being measured; the supplier's terms tell you what is being charged.