How wide is a 2x10 board?

2 x 10 kiln-dried white woods (fir, spruce, pine) will be 1 1/2 x 9 1/4"; pressure-treated 2x10s will vary from about 1 1/2 or 1 5/8 x 9 1/4 to 9 3/4, due to swelling from the high moisture content of the pressure-treatment. Rough-cut woods like cedar or redwood may also vary in their exact dimensions.