2x4 Actual Size and Dimensions

The two numbers name the piece as sawn, before a planer smooths its four faces and before it dries. The lumber standard picks this very size to define the word nominal: its text says a dry 2 by 4 is surfaced to 1-1/2 by 3-1/2 inches.

Measured as wood, the end of a dry 2x4 is 5.25 square inches against the 8 its name suggests, about 34% less. Of the four 2x sizes with a page here, it gives up the largest share.

Board feet still count the name. A foot of 2x4 is 0.67 board feet, so an 8 ft piece tallies 5.33 board feet; the board foot calculator adds up a whole list. The same nominal-against-actual gap for every size is in the nominal vs actual lumber sizes table.

Master Halco's wood book lists treated pine 2x4 rails at 8, 10, 12, 16 ft. Smooth cedar 2x4 rails run 8, 10, 12, 14, 16, 20 ft, and rough-sawn cedar 8, 10, 12, 14, 16, 18, 20 ft.

Rough cedar is thicker in the hand. PS 20-25 keeps rough lumber at least 1/8 inch over the dressed minimum in both thickness and width.

Rails: a wood fence hangs its pickets on 2x4 rails running post to post, and the Fence Calculator counts them in the lengths above.

The Western Red Cedar Lumber Association prints its 2x4 fence rail dressed to 1-9/16 by 3-9/16 inches. Those are the standard's green figures, though the association does not say the rail is green.

Braces: QUIKRETE's post-setting how-to holds a fresh post plumb with 2x4 braces on two sides that meet at a corner, left in place while the concrete sets. The Fence Post Concrete Calculator works out the bags for each hole.

For this width the cedar exception changes nothing. Table 5 of the standard gives green redwood and green cedar 2x4s the same 3-9/16 inch width as every other species.

Forms: a slab up to 3-1/2 inches thick is boarded with 2x4s, the narrowest lumber whose real width covers the pour, and the concrete slab calculator counts the boards side by side.