Measurement Guide

DIY: Nominal Lumber Size Versus

Actual Lumber Size

Every so often a homeowner tackling a new project will reach out to ask why their lumber doesn’t ﬁt the

connector. We sympathize. Lumber size can be confusing, especially when someone is ﬁrst getting started with

DIY woodworking. Nearly every single time this question comes up, it comes down to “nominal” dimensions of

the purchased lumber.

What is meant by nominal lumber size?

The nominal size is determined before the lumber

is surfaced, milled, or planed smooth. 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?

A 2×4 hasn’t measured two inches by four inches

for several decades. The lack of consistent sizing

became an issue in the early part of the 20th century

for stick-frame construction. So, in 1964, the

American Lumber Congress addressed the lumber

dimension issues by setting industry requirements

for “size standards, maximum moisture content, and

nomenclature.”

What is the actual size of a 2×4?

The actual size of a 2×4 is 1½" x 3½".

Common lumber dimensions:

Nominal Size Actual Size

1x2 ¾" x 1½"

1x3 ¾" x 2½"

1x4 ¾" x 3½"

1x6 ¾" x 5½"

1x8 ¾" x 7¼"

1x10 ¾" x 9¼"

1x12 ¾" x 11¼"

2x2 1½" x 1½"

2x3 1½" x 2½"

2x4 1½" x 3½"

2x6 1½" x 5½"

2x8 1½" x 7¼"

2x10 1½" x 9¼"

2x12 1½" x 11¼"

4x4 3½" x 3½"

4x6 3½" x 5½"

6x6 5½" x 5½"