Convert lumber nominal size to actual size (inches) instantly. Enter a value below, or use the formula and reference table further down the page.
In practice
Lumber nominal to actual size explains why a '2x4' is not 2 inches by 4 inches. The nominal name describes the rough-sawn board before it is dried and planed smooth, which removes about half an inch from each dimension: a 2x4 is really 1.5 by 3.5 inches (38 by 89 mm), a 2x6 is 1.5 by 5.5 inches and a 1x4 is 3/4 by 3.5 inches. Plan with the actual dimensions, not the nominal ones, or framing, shelving and cut lists will come out too large.
How to convert lumber nominal size to actual size (inches)
Multiply the value by 1.
in = nominal × 1Example: 10 nominal = 10 in.
Lumber Nominal Size to Actual Size (inches) conversion table
| Lumber Nominal Size (nominal) | Actual Size (inches) (in) |
|---|---|
| 1 nominal | 1 in |
| 2 nominal | 2 in |
| 3 nominal | 3 in |
| 4 nominal | 4 in |
| 5 nominal | 5 in |
| 10 nominal | 10 in |
| 15 nominal | 15 in |
| 20 nominal | 20 in |
| 25 nominal | 25 in |
| 50 nominal | 50 in |
| 100 nominal | 100 in |
Frequently asked questions
How many actual size (inches) is 1 nominal size?
1 nominal size equals 1 actual size (inches).
What is the formula to convert nominal to in?
To convert nominal to in, multiply the value by 1. The full formula is: in = nominal × 1.
How do I convert actual size (inches) back to lumber nominal size?
Use the same calculator above and type your value into the actual size (inches) field instead — it converts in both directions. Or use the reverse formula: nominal = in ÷ 1.
Is the nominal to in conversion exact?
The conversion factor used here (1) is the standard internationally defined value. Results on this page are rounded to four decimal places for readability.