What is the difference between nominal and actual dimensions

What is the difference between nominal and actual dimensions

Categories: Installation and Maintenance

Anyone who has ever gone shopping for lumber, whether it’s for construction or a small project, has encountered this issue: A piece of lumber may have a stated size such as 2x4 or 1x6, but when the lumber is actually measured, the size is a bit smaller than stated. Why isn’t the actual size listed on the lumber? Well, there is a simple explanation for this: Lumber suppliers have traditionally used nominal dimensions.

Nominal Dimensions

Nominal measurements traditionally refer to the size of the board when it was first rough cut, before it was dried and planed (smoothed).

Actual Dimensions

Actual measurements are the actual final size of the lumber after it has been dried and planed. If the final product has been planed on all four sides, it will be denoted as S4S. If only two sides are planed, it is denoted as S2S.

Common Lumber Dimensions

 Nominal Size  Actual Size 
1x2 3/4" x 1-1/2" 
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" 
                   
Difference between nominal and actual dimensions