Nominal vs Actual Lumber Sizes
Lumber is sold by its rough-sawn nominal size, but it arrives at your shop planed smaller. A 2×4 is 1.5×3.5. 3/4 plywood is usually 0.703 in. Here's the full chart and why it matters for your cut list.
Dimensional lumber (softwood 2×)
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1×2 | 3/4 × 1-1/2 | 19 × 38 |
| 1×3 | 3/4 × 2-1/2 | 19 × 64 |
| 1×4 | 3/4 × 3-1/2 | 19 × 89 |
| 1×6 | 3/4 × 5-1/2 | 19 × 140 |
| 1×8 | 3/4 × 7-1/4 | 19 × 184 |
| 1×10 | 3/4 × 9-1/4 | 19 × 235 |
| 1×12 | 3/4 × 11-1/4 | 19 × 286 |
| 2×2 | 1-1/2 × 1-1/2 | 38 × 38 |
| 2×4 | 1-1/2 × 3-1/2 | 38 × 89 |
| 2×6 | 1-1/2 × 5-1/2 | 38 × 140 |
| 2×8 | 1-1/2 × 7-1/4 | 38 × 184 |
| 2×10 | 1-1/2 × 9-1/4 | 38 × 235 |
| 2×12 | 1-1/2 × 11-1/4 | 38 × 286 |
| 4×4 | 3-1/2 × 3-1/2 | 89 × 89 |
Plywood (nominal vs measured with a caliper)
| Nominal | Typical actual | Baltic birch metric |
|---|---|---|
| 1/4 in | 0.203 in | 6 mm (0.236 in) |
| 1/2 in | 0.472 in | 12 mm (0.472 in) |
| 5/8 in | 0.578 in | 15 mm (0.591 in) |
| 3/4 in | 0.703 in | 18 mm (0.708 in) |
Hardwood grading (4/4, 5/4, 8/4)
Rough hardwood is sold in quarters of an inch. "4/4" (four-quarter) is 1 in rough, and surfaces to about 13/16 in (0.813 in) after S2S planing, or 3/4 in after S4S. "8/4" is 2 in rough, surfacing to about 1-3/4 in.
Why this breaks your cut list
If your plan calls a shelf "46 1/2 inches" between two 3/4 in sides on a 48 in cabinet, that math only works when the sides are actually 0.750 in. At 0.703 in the shelf needs to be 46.594 in — nearly 3/32 in longer — or the outer dimension shrinks.
The WoodCraft cut list calculator lets you punch in your caliper reading and rebuilds every interior part on the fly.
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