Actual vs Nominal Lumber Sizes
Lumber is sold by nominal size but the actual dimensions are smaller after drying and planing. A "2x4" is actually 1-1/2" x 3-1/2". This chart shows the actual dimensions for all common sizes.
Dimensional Lumber
| Nominal Size | Actual Size | Width (in) | Depth (in) |
|---|---|---|---|
| 1x2 | 3/4" x 1-1/2" | 0.75 | 1.5 |
| 1x3 | 3/4" x 2-1/2" | 0.75 | 2.5 |
| 1x4 | 3/4" x 3-1/2" | 0.75 | 3.5 |
| 1x6 | 3/4" x 5-1/2" | 0.75 | 5.5 |
| 1x8 | 3/4" x 7-1/4" | 0.75 | 7.25 |
| 1x10 | 3/4" x 9-1/4" | 0.75 | 9.25 |
| 1x12 | 3/4" x 11-1/4" | 0.75 | 11.25 |
| 2x2 | 1-1/2" x 1-1/2" | 1.5 | 1.5 |
| 2x3 | 1-1/2" x 2-1/2" | 1.5 | 2.5 |
| 2x4 | 1-1/2" x 3-1/2" | 1.5 | 3.5 |
| 2x6 | 1-1/2" x 5-1/2" | 1.5 | 5.5 |
| 2x8 | 1-1/2" x 7-1/4" | 1.5 | 7.25 |
| 2x10 | 1-1/2" x 9-1/4" | 1.5 | 9.25 |
| 2x12 | 1-1/2" x 11-1/4" | 1.5 | 11.25 |
| 4x4 | 3-1/2" x 3-1/2" | 3.5 | 3.5 |
| 4x6 | 3-1/2" x 5-1/2" | 3.5 | 5.5 |
| 6x6 | 5-1/2" x 5-1/2" | 5.5 | 5.5 |
| 6x8 | 5-1/2" x 7-1/2" | 5.5 | 7.5 |
| 8x8 | 7-1/2" x 7-1/2" | 7.5 | 7.5 |
Sheet Goods Thickness
| Material | Nominal | Actual |
|---|---|---|
| Plywood (standard) | 3/4" | 23/32" (0.719") |
| Plywood (1/2") | 1/2" | 15/32" (0.469") |
| Plywood (3/8") | 3/8" | 11/32" (0.344") |
| Plywood (1/4") | 1/4" | 7/32" (0.219") |
| OSB | 7/16" | 7/16" (0.4375") |
| OSB | 3/4" | 23/32" (0.719") |
| Drywall (standard) | 1/2" | 1/2" (0.5") |
| Drywall (fire-rated) | 5/8" | 5/8" (0.625") |
Why Are Actual Sizes Smaller?
When lumber is first sawed from logs, it's cut to the nominal dimension (a "2x4" starts as 2" x 4"). But then it's dried in a kiln (which shrinks it) and planed smooth on all four sides (which removes about 1/4" per face). The result is the smaller actual dimension.
The nominal size is what you ask for at the lumber yard. The actual size is what you measure and cut. Every calculation involving lumber dimensions — spans, headers, stud walls, beam sizing — must use actual dimensions.
Key Dimensions to Memorize
- 2x4 = 1.5" x 3.5" — the most common framing member
- 2x6 = 1.5" x 5.5" — exterior walls, floor joists
- 2x10 = 1.5" x 9.25" — standard floor joists
- 2x12 = 1.5" x 11.25" — stair stringers, long-span joists
- 4x4 = 3.5" x 3.5" — posts, deck columns
- 3/4" plywood = 23/32" — subfloor, sheathing
Related Calculators
Dimensions per American Softwood Lumber Standard (PS 20). Actual sizes apply to kiln-dried, surfaced (S4S) lumber. Green or rough-sawn lumber will have different dimensions.