Lumber Sizes Explained: Nominal vs Actual Dimensions

Nominal vs actual

Lumber is named by its rough-sawn size before drying and planing. After it is dried and surfaced smooth, the finished piece is smaller. The name (nominal size) is what you ask for; the actual size is what you build with.

Common dimensional lumber

• 1×4 is actually 3/4 × 3-1/2 in (19 × 89 mm)
• 2×4 is actually 1-1/2 × 3-1/2 in (38 × 89 mm)
• 2×6 is actually 1-1/2 × 5-1/2 in (38 × 140 mm)
• 2×8 is actually 1-1/2 × 7-1/4 in (38 × 184 mm)
• 2×10 is actually 1-1/2 × 9-1/4 in (38 × 235 mm)
• 2×12 is actually 1-1/2 × 11-1/4 in (38 × 286 mm)
• 4×4 is actually 3-1/2 × 3-1/2 in (89 × 89 mm)

Why it matters

Use actual dimensions when you plan cavity depths, stair rise, joist layouts and cut lists. Mixing nominal and actual numbers is a classic source of gaps and wasted material.

Length and grade

Length is usually sold in two-foot increments, and grade reflects strength and appearance. Ask our team which grade suits framing, and which is best for exposed work.