Lumber Dimensions: Nominal vs. Actual

Lumber sizes can be confusing at first. Boards are referred to by their "Nominal Size", not the actual size. This is because lumber is surfaced or planed smooth on four sides (S4S). The nominal measurement is made before the lumber is surfaced.  Always check your lumber when precise measurements are needed.

Nominal SizeActual Size
1x23/4" x 1-1/2"
1x33/4" x 2-1/2"
1x43/4" x 3-1/2"
1x63/4" x 5-1/2"
1x83/4" x 7-1/4"
1x103/4" x 9-1/4"
1x123/4" x 11-1/4"
2x21-1/2" x 1-1/2"
2x31-1/2" x 2-1/2"
2x41-1/2" x 3-1/2"
2x61-1/2" x 5-1/2"
2x81-1/2" x 7-1/4"
2x101-1/2" x 9-1/4"
2x121-1/2" x 11-1/4"
4x43-1/2" x 3-1/2"
4x63-1/2" x 5-1/2"
6x65-1/2" x 5-1/2"

Decking Planks

Nominal SizeActual Size
5/4 x 61" x 5-1/2"
6/4 x 61-5/16" x 5-1/2"
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