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Lumber Sizes and Measurement

Framing lumber is identified by the height and width of the board. The measurements used, however, may make you think you are getting cheated! A 2x4 board is actually only 1 1/2 inches by 3 1/2 inches.

The way this comes about is that when lumber is cut from the logs, it is considered "rough cut." The wood is still green and wet. Once the wood dries, it shrinks. Then, after it is dried, the wood is planed to smooth the surface and make the wood a uniform size. Once planed, the wood is considered "finished."

Thus, the nominal size of the lumber you purchase is different from the actual size. Ususally, there is 1/2 inch difference in measurements over 2 inches and 1/4 inch in measurements less than 2 inches.

When the " (inch) symbol is used is lumber measurements it indicates that you are referring to the actual size. This symbol is omitted when referring to the nominal size.

Plywood Lumber Standard Sizes

Standard plywood comes in sheets that measure 4 feet wide and 8 feet long. Plywood is generally available in thicknesses of 1/8", 1/4", 3/8", 1/2", 5/8", and 3/4".

Many hardware stores sell pre-cut plywood in 2'x2', 2'x4' and 4'x4' sizes.

Finished Lumber Sizes

Framing lumber, is usually sold by the piece in standard lengths and dimension. The lumber is generally sold in lengths of 6', 8', 10', 12' and 16'.

This table shows the Nominal and Actual Measurements of many standard sizes of lumber.

NOMINAL SIZE ACTUAL SIZE
1x1 3/4" x 3/4"

1x3 3/4" x 2 1/2"
1x4 3/4" x 3 1/2"
1x6 3/4" x 5 1/2"

1x8

3/4" x 7 1/4"
1x10 3/4" x 9 1/4"
1x12 3/4" x 11 1/4"
2x2

1 1/2" x 1 1/2"
2x3 1 1/2" x 2 1/2"
2x4 1 1/2" x 3 1/2"
2x6 1 1/2" x 5 1/2"

2x8 1 1/2" x 7 1/4"
2x10 1 1/2" x 9 1/4"
2x12 1 1/2" x 11 1/4"

4x4

3 1/2" x 3 1/2"
4x6 3 1/2" x 5 1/2"
6x6 5 1/2" x 5 1/2"
8x8

7 1/4" x 7 1/4"


There is a standard lumber size known as 5/4 that is an actual 1" thick. This size is often used for deck surface boards.

Unfinished rough lumber sizes

Standard thicknesses for rough lumber are 3/8", 1/2", 5/8", 3/4", 1", 1-1/4", 1-1/2", 1-3/4", 2", 2-1/2", 3", 3-1/2", 4", 4-1/2", 5", 5-1/2", and 6". One inch and thicker may also be expressed in quarter inches as follows: 4/4, 5/4, 6/4, 7/4, 8/4, 10/4, 12/4, 14/4, 16/4, 18/4, 20/4, 22/4 and 24/4.

For More Information


National Hardware Lumber Grading Rules (pdf)
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