Lumber Dimension Converter
Convert between nominal and actual lumber dimensions, and calculate board feet from length, width, and thickness.
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Enter board dimensions to calculate board feet. All fields update each other.
Lumber dimensions in North America use a nominal naming system that differs from the actual measured size. When you buy a “2x4” at the lumber yard, the board is NOT 2 inches by 4 inches. The nominal size refers to the rough-cut dimension before the wood is dried and planed smooth.
How nominal vs actual works: After rough-cutting, lumber is kiln-dried and planed (surfaced) on all four sides. This process removes approximately 1/2 inch from each dimension for boards under 2 inches nominal, and 3/4 inch for boards 2 inches and larger.
Common nominal to actual conversions:
| Nominal | Actual (inches) | Actual (mm) |
|---|---|---|
| 1 x 2 | 3/4 x 1-1/2 | 19 x 38 |
| 1 x 4 | 3/4 x 3-1/2 | 19 x 89 |
| 1 x 6 | 3/4 x 5-1/2 | 19 x 140 |
| 2 x 2 | 1-1/2 x 1-1/2 | 38 x 38 |
| 2 x 4 | 1-1/2 x 3-1/2 | 38 x 89 |
| 2 x 6 | 1-1/2 x 5-1/2 | 38 x 140 |
| 2 x 8 | 1-1/2 x 7-1/4 | 38 x 184 |
| 2 x 10 | 1-1/2 x 9-1/4 | 38 x 235 |
| 2 x 12 | 1-1/2 x 11-1/4 | 38 x 286 |
| 4 x 4 | 3-1/2 x 3-1/2 | 89 x 89 |
| 6 x 6 | 5-1/2 x 5-1/2 | 140 x 140 |
Board feet calculation: A board foot is a unit of volume used to measure lumber. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick (144 cubic inches).
The formula is:
- Board feet = (thickness in inches x width in inches x length in feet) / 12
For example, an 8-foot-long 2x6 (using nominal dimensions) contains:
- (2 x 6 x 8) / 12 = 8 board feet
Important notes for woodworkers:
- Board foot calculations traditionally use nominal dimensions, not actual dimensions.
- Hardwood lumber is typically sold by the board foot, while softwood (construction lumber) is sold by the linear foot or per piece.
- When estimating material for a project, add 15-20% for waste from cutting, defects, and mistakes.
- Metric countries use cubic meters for lumber volume, where 1 board foot equals approximately 0.002360 cubic meters.