Quick Answer
Exact Dimensions of a 2×4
The **exact finished size** of a standard 2×4 is 1.5 inches thick × 3.5 inches wide.
In metric, that’s 38 mm × 89 mm.
These dimensions apply to kiln-dried, surfaced lumber in the U.S. and Canada.
Exact vs nominal
The **exact dimensions** are smaller than the nominal (2″ × 4″) because lumber is milled down after drying to make it straight, smooth, and uniform. This reduction gives the consistent 1.5″ × 3.5″ measurement you find at hardware stores.
Exact dimensions table
| Dimension | Inches | Millimeters | Centimeters |
|---|---|---|---|
| Thickness | 1.5″ | 38 | 3.8 |
| Width | 3.5″ | 89 | 8.9 |
Lengths are sold separately and can range from 2 feet to over 20 feet.
FAQ: Exact dimensions of a 2×4
Are exact dimensions consistent across brands?
Yes—major lumber suppliers in the U.S. follow the same standard for surfaced boards.
Do metric-sized 2×4s exist?
In countries using metric, boards may be cut to metric nominal sizes, but U.S. standard 2×4 conversions remain 38 × 89 mm.