Quick Answer
2×4 Width: 3.5 inches (89 mm)
The actual width of a 2×4 is 3.5 inches, which is 89 mm.
The matching thickness is 1.5 inches (38 mm). “2×4” is the nominal name used in stores; the finished size is smaller.
Exact width & thickness
| Measurement | Inches | Millimeters | Centimeters |
|---|---|---|---|
| 2×4 width (actual) | 3.5″ | 89 | 8.9 |
| 2×4 thickness (actual) | 1.5″ | 38 | 3.8 |
Also searched as: actual width of 2×4, 2×4 real dim width, and width of a 2×4 in mm.
Why the 2×4 width is 3.5″
“2×4” is the nominal (rough-cut) name. After kiln drying and planing the board smooth (surfacing on four sides, or S4S), material is removed from each face, leaving a finished width of 3.5 inches and thickness of 1.5 inches. This has been the North American standard for decades.
Compare width across common sizes
| Nominal | Actual Width (in) | Actual Width (mm) | Details |
|---|---|---|---|
| 2×4 | 3.5 | 89 | 2×4 actual size |
| 2×6 | 5.5 | 140 | 2×6 actual size |
| 2×8 | 7.25 | 184 | 2×8 actual size |
| 2×10 | 9.25 | 235 | 2×10 actual size |
| 4×4 | 3.5 | 89 | 4×4 actual size |
FAQ: 2×4 width
What is the actual width of a 2×4?
3.5 inches (89 mm). Thickness is 1.5 inches (38 mm).
Is the width always 3.5″?
For standard North American softwood framing lumber, yes. Small variations can occur from moisture and milling tolerances.
Why doesn’t a 2×4 measure 4 inches wide?
Because the “2×4” label is nominal. Drying and planing reduce the board to its finished size of 1.5″ × 3.5″.