North America lumber sizes are usually given in "nominal" measurements, which is the size of lumber cut from moist logs. However, the actual size of lumber is less than its nominal size (due to shrinkage and surface planning at mills). The table below provides some common North American Lumber nominal sizes and their equivalent actual size.
Nominal Size  Standard Dressed Size
in. x in.

Standard Dressed Size
mm x mm

Area of Section
in.^{2}



Boards


1 x 3  3/4 x 21/2  19 x 63  1.875  
1 x 4  3/4 x 31/2  19 x 89  2.625  
1 x 6  3/4 x 51/2  19 x 140  3.781  
1 x 8  3/4 x 71/4  19 x 184  5.438  
1 x 10  3/4 x 91/4  19 x 235  6.938  
1 x 12  3/4 x 111/4  19 x 286  8.438  
Dimension Lumber and Decking


2 x 3  11/2 x 21/2  38 x 64  3.750  
2 x 4  11/2 x 31/2  38 x 89  5.250  
2 x 5  11/2 x 41/2  38 x 114  6.750  
2 x 6  11/2 x 51/2  38 x 140  8.250  
2 x 8  11/2 x 71/4  38 x 184  10.88  
2 x 10  11/2 x 91/4  38 x 235  13.88  
2 x 12  11/2 x 111/4  38 x 286  16.88  
2 x 14  11/2 x 131/4  38 x 337  19.88  
3 x 4  21/2 x 31/2  64 x 89  8.75  
3 x 5  21/2 x 41/2  64 x 114  11.25  
3 x 6  21/2 x 51/2  64 x 140  13.75  
3 x 8  21/2 x 71/4  64 x 184  18.13  
3 x 10  21/2 x 91/4  64 x 235  23.13  
3 x 12  21/2 x 111/4  64 x 286  28.13  
3 x 14  21/2 x 131/4  64 x 337  33.13  
3 x 16  21/2 x 151/4  64 x 387  38.13  
4 x 4  31/2 x 31/2  89 x 89  12.25  
4 x 5  31/2 x 41/2  89 x 114  15.75  
4 x 6  31/2 x 51/2  89 x 140  19.25  
4 x 8  31/2 x 71/4  89 x 184  25.38  
4 x 10  31/2 x 91/4  89 x 235  32.38  
4 x 12  31/2 x 111/4  89 x 286  39.38  
4 x 14  31/2 x 131/4  89 x 337  46.38  
4 x 16  31/2 x 151/4  89 x 387  53.38  
Post and Timber


5 x 5  41/2 x 41/2  114 x 114  20.25  
6 x 6  51/2 x 51/2  140 x 140  30.25  
6 x 8  51/2 x 71/2  140 x 190  41.25  
8 x 8  71/2 x 71/2  190 x 190  56.25  
8 x 10  71/2 x 91/2  190 x 241  71.25  
10 x 10  91/2 x 91/2  241 x 241  90.25  
10 x 12  91/2 x 111/2  241 x 292  109.3  
12 x 12  111/2 x 111/2  292 x 292  132.3  
12 x 14  111/2 x 131/2  292 x 343  155.3  
14 x 14  131/2 x 131/2  343 x 343  182.3  
14 x 16  131/2 x 151/2  343 x 394  209.3 