Reference chart
Lumber Size Chart: Nominal vs Actual
A "2x4" isn't 2 by 4. Every dimensional board is named for its rough green size, then dried and planed smaller. This chart gives the actual surfaced dimensions in inches for the sizes you'll meet at any North American yard.
How do I use this size chart when I'm buying?
The first thing I tell anyone new to a lumber yard is that the chart below settles arguments, not the calculator. When a builder swears his joists won't fit, nine times out of ten he measured an actual 9.25″ 2x10 and expected a clean 10 inches. So I keep this table for fit questions, and I keep board-foot math on a separate page — if you're chasing the pricing number instead, start with how to calculate board feet, because that's a different question than "how wide is this board really."
A quick story on why the gap matters. I once signed off on a deck-skirting order where the carpenter had planned his gaps around a 6-inch 1x6. The actual board is 5.5″ so across a 40-ft run he came up about 3.3 ft short of coverage (estimate) — roughly two extra boards he hadn't bought. Half an inch per board sounds like nothing until it stacks across a whole job, and that's the exact mistake this chart exists to prevent.
So my habit at the counter is blunt: I never quote a fit dimension from the nominal name. I read the actual column out loud, write it on the cut list, and let the customer plan clearances from the real number. For thickness it's even simpler — every 2x is 1.5″ every 1x is 0.75″ no exceptions in softwood. It's the width that drifts, and the chart keeps me honest on it.
What are the nominal vs actual sizes?
| Nominal | Actual (inches) |
|---|---|
| 1x2 | 0.75 × 1.5 |
| 1x3 | 0.75 × 2.5 |
| 1x4 | 0.75 × 3.5 |
| 1x6 | 0.75 × 5.5 |
| 1x8 | 0.75 × 7.25 |
| 1x10 | 0.75 × 9.25 |
| 1x12 | 0.75 × 11.25 |
| 2x2 | 1.5 × 1.5 |
| 2x4 | 1.5 × 3.5 |
| 2x6 | 1.5 × 5.5 |
| 2x8 | 1.5 × 7.25 |
| 2x10 | 1.5 × 9.25 |
| 2x12 | 1.5 × 11.25 |
| 4x4 | 3.5 × 3.5 |
| 6x6 | 5.5 × 5.5 |
What is the pattern to remember?
Thickness loses ¼″ (a 2x is 1.5″). Width loses ½″ up to 6″ nominal, then ¾″ at 8″ and wider — that's why a 2x8 is 7.25″ not 7.5″. The full reasoning, plus when actual size actually matters for your math, is in nominal vs actual dimensions.
Which size do I use for board feet?
Use the nominal size for softwood board-foot math, because that's how it's priced. Actual size matters for fit — joist depth, drawer clearances — not for the yard ticket. Hardwood is different; it's billed on surface measure, covered in the hardwood thickness guide. Grab quick multipliers on the cheat sheet.