2×4 Actual Dimension: 1.5″ × 3.5″

Q: What are the actual dimensions of a 2×4?

The actual dimensions of a 2×4 are 1.5 inches by 3.5 inches (38 mm × 89 mm).

Q: Does it vary by country?

Yes. Canada and the U.S. use the same standard, but other countries use different nominal sizes.

Q: When did these dimensions become standard?

They became standard in the mid-20th century when milling and drying processes were standardized.

The actual dimensions of a 2×4 are 1.5 inches thick by 3.5 inches wide (38 mm × 89 mm). The length varies by what you buy — 8, 10, 12 feet, etc. This “true size” is smaller than the nominal name because of how lumber is processed.

Actual 2×4 size: 1.5″ × 3.5″ (38 mm × 89 mm).

Exact 2×4 dimensions

Measurement	Inches	Millimeters	Centimeters
Thickness	1.5″	38	3.8
Width	3.5″	89	8.9

Other names: exact dimensions of 2×4, true size of a 2×4.

Why the “actual” size is smaller

Lumber is cut to its nominal size while green (freshly sawn). It’s then kiln dried and planed smooth, which removes material from each side. This process turns a rough 2″ × 4″ into a finished 1.5″ × 3.5″ board.

Compare actual dimensions across common sizes

Nominal	Actual (inches)	Actual (mm)
2×4	1.5 × 3.5	38 × 89
2×6	1.5 × 5.5	38 × 140
2×8	1.5 × 7.25	38 × 184

FAQ: 2×4 actual dimension

What are the actual dimensions of a 2×4?

1.5 inches by 3.5 inches (38 mm × 89 mm).

Does it vary by country?

Yes. Canada and the U.S. share the same standard, but some countries use metric-based nominal sizes.

When did these dimensions become standard?

They’ve been the North American standard since the mid-20th century, after milling and drying practices were standardized.