end view of log sliced into boards

Common Lumber Dimensions

Nominal vs. actual lumber dimensions:
Why a 2" × 4" is not always a 2" × 4"

Lumber sizes are usually given in "nominal" measurements. The nominal measurements are a board's size before it has been planed smooth (surfaced) on all 4 sides. The actual measurements are the final size. If your project calls for precise measurements, be sure to check your lumber before purchasing.

Dimensional Lumber
Nominal Size Actual Size
1×2 3/4" × 1-1/2"
1×3 3/4" × 2-1/2"
1×4 3/4" × 3-1/2"
1×6 3/4" × 5-1/2"
1×8 3/4" × 7-1/4"
1×10 3/4" × 9-1/4"
1×12 3/4" × 11-1/4"
2×2 1-1/2" × 1-1/2"
2×3 1-1/2" × 2-1/2"
2×4 1-1/2" × 3-1/2"
2×6 1-1/2" × 5-1/2"
2×8 1-1/2" × 7-1/4"
2×10 1-1/2" × 9-1/4"
2×12 1-1/2" × 11-1/4"
4×4 3-1/2" × 3-1/2"
4×6 3-1/2" × 5-1/2"
6×6 5-1/2" × 5-1/2"

Decking Planks
Nominal Size Actual Size
5/4 × 6 1" × 5-1/2"
6/4 × 6 1-5/16" × 5-1/2"