DIMENSIONAL LUMBER 2x3 to 2x12 Nominal Sizes
The actual size of dimensional lumber in the North American lumber sizing system is different than the names of the boards. A 2x4, for example, is actually a "one and a half by three and a half". Wood is a natural product and it shrinks as it dries.
For more information and a complete chart of lumber sizes in North America see, https://en.wikipedia.org/wiki/Lumber
"Jindupe" by Lauren Duski