How board feet are calculated
A board foot is a volume of wood: a piece 1 inch thick, 12 inches wide and 12 inches long. That is 144 cubic inches. To find the board feet in any board, multiply thickness and width in inches by length in feet, then divide by 12.
board feet = thickness (in) × width (in) × length (ft) ÷ 12
total = board feet per board × number of boards
Worked example
You need ten 2×6 boards, each 8 ft long. One board is 2 × 6 × 8 ÷ 12 = 8 board feet, so ten boards are 80 board feet. If your yard quotes $4.00 per board foot (a figure picked only to show the math), the order costs $320.00. In volume that is 6.67 cubic feet, or 0.189 m³, and 80 ft (24.4 m) of boards laid end to end.
Nominal or actual size?
Softwood framing lumber is named by its nominal size, the size before drying and planing. A 2×4 actually measures about 1½ × 3½ inches. By long trade convention, board feet for dimension lumber are figured on the nominal size, so a 2×4 that is 8 ft long counts as 5.33 board feet even though less wood is there. This calculator follows that convention: enter 2 and 4, not 1.5 and 3.5.
Hardwood is different. It is sold by rough thickness in quarters of an inch: 4/4 (one inch), 5/4, 6/4 and 8/4. A 4/4 board planed smooth may end up near 13/16 in thick, but it is still sold as 1 inch. Enter the quarter size as inches, for example 1.25 for 5/4.
Board feet in common sizes
| Board (nominal) | Actual size | Board feet |
|---|---|---|
| 1×6, 8 ft | ¾ × 5½ in | 4 |
| 2×4, 8 ft | 1½ × 3½ in | 5.33 |
| 2×6, 8 ft | 1½ × 5½ in | 8 |
| 2×8, 8 ft | 1½ × 7¼ in | 10.67 |
| 2×10, 12 ft | 1½ × 9¼ in | 20 |
| 2×12, 16 ft | 1½ × 11¼ in | 32 |
| 4×4, 8 ft | 3½ × 3½ in | 10.67 |
| 6×6, 8 ft | 5½ × 5½ in | 24 |
Metric conversions
One board foot is 0.00236 m³, and one cubic meter is about 424 board feet. In Australia most framing timber is sold by the linear meter in sizes such as 90 × 45 mm, so board feet rarely appear on a quote there. Canadian yards use the same nominal names as the US. If you switch to metric, the calculator still reports board feet, because that is how hardwood is traded, and adds the volume in m³ based on the nominal size.
Common mistakes
- Length in inches. The formula divides by 12 because length is in feet. If you measured length in inches, divide by 144 instead: a 2×6 that is 96 in long is 2 × 6 × 96 ÷ 144 = 8 board feet.
- Using actual dimensions for framing lumber. 1.5 × 5.5 × 8 ÷ 12 gives 5.5 board feet for an 8 ft 2×6, not the 8 the yard will bill. Your total will be low and quotes will not match.
- Forgetting offcuts. Board feet measure what you buy, not what ends up in the project. Add waste before you order, not after.
Tips before you order
- Ask how your supplier prices each item. Hardwood is almost always priced per board foot; framing lumber at a home center is usually priced per piece.
- Hardwood often comes in random widths and lengths. Measure each board, or ask for the board-foot tally on the ticket, and add about 20 to 30 percent for defects and cutting waste on furniture work.
- Price per board foot changes with thickness, grade and species. A higher grade such as FAS has fewer knots and costs more per board foot.
- To compare a per-piece price with a per-board-foot price, divide the piece price by the board feet in one piece.
Frequently asked questions
How many board feet are in a 2×4×8?
An 8 ft 2×4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet, using the nominal size as the trade does.
How do I convert board feet to cubic meters?
Multiply board feet by 0.00236. For example, 80 board feet is about 0.189 m³. One cubic meter is about 424 board feet.
Is a board foot the same as a linear foot?
No. A linear foot is just length. A board foot is volume, so one linear foot of 2×6 is 1 board foot but one linear foot of 2×4 is only 0.67 board feet.
Should I use actual or nominal dimensions?
Use nominal dimensions for softwood lumber and the rough quarter thickness for hardwood. That matches how lumber is tallied and priced.