How to Calculate Board Feet
A board foot is a unit of volume used to price hardwood lumber. Hardwoods are sold by the board foot regardless of dimensions, so accurate calculations matter for budgeting woodworking projects.
Board Foot Formula
Board Feet=Tin×Win×Lft12
One board foot equals 144 cubic inches: 1 inch thick by 12 inches wide by 12 inches long. To convert to cubic meters, multiply board feet by 0.00236.
Quarter-Inch Thickness System
Hardwood lumber is sold in quarter-inch nominal thicknesses:
4/4
3/4 in S4S
Most common
5/4
1-1/16 in S4S
Stair treads
6/4
1-5/16 in S4S
Tabletops
8/4
1-3/4 in S4S
Legs, posts
Nominal vs. Surfaced
Use nominal (rough) thickness when calculating board feet for pricing. Surfaced four sides (S4S) lumber is about 1/4 inch smaller in each dimension after planing. The price still uses the nominal size.Common Hardwood Prices (2026)
| Species | Price/BF |
|---|---|
| Poplar | $3 to $5 |
| Red Oak | $5 to $8 |
| Cherry | $7 to $12 |
| Walnut | $10 to $15 |
| Mahogany | $12 to $20 |
Plan for Defects
Add 20 to 30 percent waste when buying hardwood. Boards have knots, splits, sapwood, and grain mismatches you will work around. For figured lumber where you select around defects, increase to 40 percent.Lumber Grades (NHLA Rules)
| Grade | Clear Face % | Best For |
|---|---|---|
| FAS (Firsts & Seconds) | 83%+ | High-end furniture, millwork |
| Select | 83%+ (one face) | Furniture with one visible side |
| #1 Common | 66%+ | Cabinets, shorter pieces |
| #2 Common | 50%+ | Flooring, paintable projects |
Sample Board Foot Calculations
- 1 in x 6 in x 8 ft = (1 x 6 x 8) / 12 = 4 BF
- 2 in x 10 in x 12 ft = (2 x 10 x 12) / 12 = 20 BF
- 4/4 x 8 in x 10 ft = (1 x 8 x 10) / 12 = 6.67 BF
- 8/4 x 12 in x 8 ft = (2 x 12 x 8) / 12 = 16 BF
Random Widths and Lengths (RWL)
Hardwood is typically sold in random widths (3 to 12 inches) and random lengths (4 to 16 ft). You cannot order specific dimensions from most hardwood dealers. Plan projects around common widths by gluing up panels or buying extra for width selection.