Dimensional Lumber Sizes

One of the biggest misconceptions to people unfamiliar with woodworking or carpentry is that a 2×4 (pronounced “two by four”) is 2 inches thick and 4 inches wide. The vast majority of 2x4s purchased in the United States are 1-1/2″x3-1/2.” In fact most softwood used in construction is consistently undersized as a result of the manufacturing process. Below is a chart of the nominal dimensions and the true dimensions of lumber commonly used in construction, crating, and industrial woodworking.

This chart is adapted from the American Softwood Lumber Standard (PS-20) published by NIST. The following table is a simplification of the table found in that standard. Refer to PS-20 for anything other than casual reference.

Boards

Nominal DimensionTrue Dimension
3/8×2 5/16×1-1/2
3/8×3 5/16×2-1/2
3/8×4 5/16×3-1/2
3/8×5 5/16×4-1/4
3/8×6 5/16×5-1/2
3/8×7 5/16×6-1/2
3/8×8 5/16×7-1/4
3/8×9 5/16×8-1/4
3/8×10 5/16×9-1/4
3/8×11 5/16×10-1/4
3/8×12 5/16×11-1/4
3/8×14 5/16×13-1/4
3/8×16 5/16×15-1/4
1/2×2 7/16×1-1/2
1/2×3 7/16×2-1/2
1/2×4 7/16×3-1/2
1/2×5 7/16×4-1/4
1/2×6 7/16×5-1/2
1/2×7 7/16×6-1/2
1/2×8 7/16×7-1/4
1/2×9 7/16×8-1/4
1/2×10 7/16×9-1/4
1/2×11 7/16×10-1/4
1/2×12 7/16×11-1/4
1/2×14 7/16×13-1/4
1/2×16 7/16×15-1/4
5/8×2 9/16×1-1/2
5/8×3 9/16×2-1/2
5/8×4 9/16×3-1/2
5/8×5 9/16×4-1/4
5/8×6 9/16×5-1/2
5/8×7 9/16×6-1/2
5/8×8 9/16×7-1/4
5/8×9 9/16×8-1/4
5/8×10 9/16×9-1/4
5/8×11 9/16×10-1/4
5/8×12 9/16×11-1/4
5/8×14 9/16×13-1/4
5/8×16 9/16×15-1/4
3/4×2 5/8×1-1/2
3/4×3 5/8×2-1/2
3/4×4 5/8×3-1/2
3/4×5 5/8×4-1/4
3/4×6 5/8×5-1/2
3/4×7 5/8×6-1/2
3/4×8 5/8×7-1/4
3/4×9 5/8×8-1/4
3/4×10 5/8×9-1/4
3/4×11 5/8×10-1/4
3/4×12 5/8×11-1/4
3/4×14 5/8×13-1/4
3/4×16 5/8×15-1/4
1×2 3/4×1-1/2
1×3 3/4×2-1/2
1×4 3/4×3-1/2
1×5 3/4×4-1/4
1×6 3/4×5-1/2
1×7 3/4×6-1/2
1×8 3/4×7-1/4
1×9 3/4×8-1/4
1×10 3/4×9-1/4
1×11 3/4×10-1/4
1×12 3/4×11-1/4
1×14 3/4×13-1/4
1×16 3/4×15-1/4
1-1/4×2 1×1-1/2
1-1/4×3 1×2-1/2
1-1/4×4 1×3-1/2
1-1/4×5 1×4-1/4
1-1/4×6 1×5-1/2
1-1/4×7 1×6-1/2
1-1/4×8 1×7-1/4
1-1/4×9 1×8-1/4
1-1/4×10 1×9-1/4
1-1/4×11 1×10-1/4
1-1/4×12 1×11-1/4
1-1/4×14 1×13-1/4
1-1/4×16 1×15-1/4
1-1/2×2 1-1/4×1-1/2
1-1/2×3 1-1/4×2-1/2
1-1/2×4 1-1/4×3-1/2
1-1/2×5 1-1/4×4-1/4
1-1/2×6 1-1/4×5-1/2
1-1/2×7 1-1/4×6-1/2
1-1/2×8 1-1/4×7-1/4
1-1/2×9 1-1/4×8-1/4
1-1/2×10 1-1/4×9-1/4
1-1/2×11 1-1/4×10-1/4
1-1/2×12 1-1/4×11-1/4
1-1/2×14 1-1/4×13-1/4
1-1/2×16 1-1/4×15-1/4

Dimensional Lumber (Construction Lumber)

Nominal DimensionTrue Dimension
2×2 1-1/2×1-1/2
2×2-1/2 1-1/2×2
2×3 1-1/2×2-1/2
2×3-1/2 1-1/2×3
2×4 1-1/2×3-1/2
2×4-1/2 1-1/2×4
2×5 1-1/2×4-1/2
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
2×14 1-1/2×13-1/4
2×16 1-1/2×15-1/4
2-1/2×2 2×1-1/2
2-1/2×2-1/2 2×2
2-1/2×3 2×2-1/2
2-1/2×3-1/2 2×3
2-1/2×4 2×3-1/2
2-1/2×4-1/2 2×4
2-1/2×5 2×4-1/2
2-1/2×6 2×5-1/2
2-1/2×8 2×7-1/4
2-1/2×10 2×9-1/4
2-1/2×12 2×11-1/4
2-1/2×14 2×13-1/4
2-1/2×16 2×15-1/4
3×2 2-1/2×1-1/2
3×2-1/2 2-1/2×2
3×3 2-1/2×2-1/2
3×3-1/2 2-1/2×3
3×4 2-1/2×3-1/2
3×4-1/2 2-1/2×4
3×5 2-1/2×4-1/2
3×6 2-1/2×5-1/2
3×8 2-1/2×7-1/4
3×10 2-1/2×9-1/4
3×12 2-1/2×11-1/4
3×14 2-1/2×13-1/4
3×16 2-1/2×15-1/4
3-1/2×2 3×1-1/2
3-1/2×2-1/2 3×2
3-1/2×3 3×2-1/2
3-1/2×3-1/2 3×3
3-1/2×4 3×3-1/2
3-1/2×4-1/2 3×4
3-1/2×5 3×4-1/2
3-1/2×6 3×5-1/2
3-1/2×8 3×7-1/4
3-1/2×10 3×9-1/4
3-1/2×12 3×11-1/4
3-1/2×14 3×13-1/4
3-1/2×16 3×15-1/4
4×2 3-1/2×1-1/2
4×2-1/2 3-1/2×2
4×3 3-1/2×2-1/2
4×3-1/2 3-1/2×3
4×4 3-1/2×3-1/2
4×4-1/2 3-1/2×4
4×5 3-1/2×4-1/2
4×6 3-1/2×5-1/2
4×8 3-1/2×7-1/4
4×10 3-1/2×9-1/4
4×12 3-1/2×11-1/4
4×14 3-1/2×13-1/4
4×16 3-1/2×15-1/4
4-1/2×2 4×1-1/2
4-1/2×2-1/2 4×2
4-1/2×3 4×2-1/2
4-1/2×3-1/2 4×3
4-1/2×4 4×3-1/2
4-1/2×4-1/2 4×4
4-1/2×5 4×4-1/2
4-1/2×6 4×5-1/2
4-1/2×8 4×7-1/4
4-1/2×10 4×9-1/4
4-1/2×12 4×11-1/4
4-1/2×14 4×13-1/4
4-1/2×16 4×15-1/4

Timber Dimensions

Nominal DimensionTrue Dimension
5×54-1/2×4-1/2
5×64-1/2×5-1/2
6×55-1/2×4-1/2
6×65-1/2×5-1/2

The standard allows for much larger boards than listed above, but their specifications are omitted due to their rarity.