DIY: Nominal Lumber Size Versus Actual Lumber Size

nominal size measurements

Every so oftena homeowner tackling a new project will reach out to ask why their lumber doesn’t fit the connector. We sympathize. Lumber sizes can be confusing, especially when someone is first getting started with DIY woodworking.Nearly every single timethis question comes up,it comes down to “nominal” dimensions of the purchased lumber.

What is meant by nominallumbersize?

The nominal size is determined before the lumber is surfaced, milled, or planedsmooth. This finishing process gives lumber a uniform profile, so there’s consistency when you go to the lumberyard. The finished size is the “actual lumber size” (sometimes referred to as the “dressed lumber size”).

Why isn’t a 2×4 actually a 2×4?

A2×4 hasn’t measured two inches by four inches forseveral decades. The lack of consistent sizingbecame an issue in the early part of the 20thcenturyforstickframe construction.So,in 1964, the American Lumber Congress addressed the lumber dimension issues bysetting industry requirementsfor “size standards, maximum moisture content, and nomenclature.”

What is theactualsize of a 2×4?

The actual sizeofa 2×4 is 1½x 3½.

Common lumber dimensions:

Nominal Size Actual Size
1×2 3/4″ × 1½
1×3 3/4″ × 2½
1×4 3/4″ × 3½
1×6 3/4″ × 5½
1×8 3/4″ × 7¼
1×10 3/4″ × 9¼
1×12 3/4″ × 11¼
2×2 1½” × 1½
2×3 1½” × 2½
2×4 1½” × 3½
2×6 1½” × 5½
2×8 1½” × 7¼
2×10 1½” × 9¼
2×12 1½” × 11¼
4×4 3½” × 3½
4×6 3½” × 5½
6×6 5½” × 5½

Need another explanation? David Lynch took a shot at articulating the issue of lumber dimensions inTwin Peaks: