Nominal vs Actual Lumber Size Chart
Every dimensional lumber size is sold under a name that does not match its real dimensions. This chart gives you the actual milled size, the cross-section area, and how much less the board actually covers than its name suggests.
| Nominal | Actual thickness | Actual width | Cross-section | Coverage vs nominal |
|---|---|---|---|---|
| 1 × 2 | 0.75" | 1.5" | 1.13 sq in | 75.0% |
| 1 × 3 | 0.75" | 2.5" | 1.88 sq in | 83.3% |
| 1 × 4 | 0.75" | 3.5" | 2.63 sq in | 87.5% |
| 1 × 6 | 0.75" | 5.5" | 4.13 sq in | 91.7% |
| 1 × 8 | 0.75" | 7.25" | 5.44 sq in | 90.6% |
| 1 × 10 | 0.75" | 9.25" | 6.94 sq in | 92.5% |
| 1 × 12 | 0.75" | 11.25" | 8.44 sq in | 93.8% |
| 2 × 2 | 1.5" | 1.5" | 2.25 sq in | 75.0% |
| 2 × 3 | 1.5" | 2.5" | 3.75 sq in | 83.3% |
| 2 × 4 | 1.5" | 3.5" | 5.25 sq in | 87.5% |
| 2 × 6 | 1.5" | 5.5" | 8.25 sq in | 91.7% |
| 2 × 8 | 1.5" | 7.25" | 10.88 sq in | 90.6% |
| 2 × 10 | 1.5" | 9.25" | 13.88 sq in | 92.5% |
| 2 × 12 | 1.5" | 11.25" | 16.88 sq in | 93.8% |
| 4 × 4 | 3.5" | 3.5" | 12.25 sq in | 87.5% |
| 4 × 6 | 3.5" | 5.5" | 19.25 sq in | 91.7% |
| 4 × 8 | 3.5" | 7.25" | 25.38 sq in | 90.6% |
| 4 × 10 | 3.5" | 9.25" | 32.38 sq in | 92.5% |
| 4 × 12 | 3.5" | 11.25" | 39.38 sq in | 93.8% |
| 6 × 6 | 5.5" | 5.5" | 30.25 sq in | 91.7% |
| 8 × 8 | 7.25" | 7.25" | 52.56 sq in | 90.6% |
Why the gap exists
Rough lumber is sawn oversize on purpose. A board called 4/4 is cut about 1 inch thick so that after drying shrinkage and surfacing, it lands near the finished ¾ inch. The oversize allowance is exactly the gap you see in the table.
Which numbers matter in practice
- Coverage calculations — when boards tile a surface, use actual width. This is the single biggest source of under-ordering.
- Structural sizing — joist and beam tables are already based on actual cross section. Use the tables directly.
- Board foot pricing — the formula uses nominal thickness for rough lumber because that is how it is billed.
- Floor height — a 2×4 laid flat is 1½ inches, not 2. Three layers of subfloor plus 2×4 blocking costs you half an inch you may not have planned for.
Where to buy
Compare current pricing across major suppliers — prices vary by region and season.
Related tools
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