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Actual and Advertised Lumber Dimensions Never Match

When is a 2×4 not 2 inches by4 inches? When you actually measure it! In fact, all dimensional lumber commonly used in building construction is called by it’s nominal name rather than its actual dimensions, which are always smaller.

Lumber is marketed with a nominal name, which is basically a nice round number that’s easy to remember but not really the actual measurement.

There are standardized requirements on what dimensions wood has to be when it reaches the customer, the below table lists nominal names and their actual standardized real dimensions:

Nominal name Actual dimenion
2 1 ½ inches
3 2 ½ inches
4 3 ½ inches
6 5 ½ inches
8 7 ½ inches
10 9 ½ inches
12 11 ½ inches

For example: A 2 by 4 is not 2 inches by 4 inches, it’s actually only 1 ½ x inches by 3 ½ inches because the 2×4 name describes the lumber’s size before drying and planing for straightness. 2×4, 2×6, 4×4, etc. are only nominal names and do not ever describe the lumber’s actual dimensions.


  • History of Yard Lumber Sizes (link is external). L. W. Smith & L. W. Wood, U.S. Department of Agriculture. Accessed 31 December, 2013. – Overview: In-depth article from the U.S. Forest Service. Details include history of lumber production process, nominal names and corresponding actual dimensions.