Why is 3 read as cubed when used as an exponent?

Volume is often measured in "cubic" units. That is to say a cube of a given size. e.g cubic centimeters, cubic feet. To calculate the volume of a rectangular prism, you would multiply length x witdth x height. If the length, width, and height are equal, you would multiply that value by itself twice. e.g. 2 x 2 x 2. This expression can also be written with an exponent of 3 (23) or 2 cubed. The same logic applies to an exponent of 2 used in expressions of area (length x width.) If length and width are equal, it is a square, hence "square feet" or ft2.