Volume is the amount of space within a three-dimensional solid. To calculate the volume of a box, multiply its length by its width by its height.

For example, a box is 3 feet long, 4 feet wide, and 5 feet high. To calculate the volume, do the following:

length = 3 feet
width  = 4 feet
height = 5 feet
volume = 3 feet × 4 feet × 5 feet = 60 cubic feet

To understand why the length, width, and height are multiplied, think of a box as a stack of three-dimensional rectangles, and each rectangle as a grid of smaller cubes. In the example above, think of the box as having 5 rectangles, with each rectangle having 3 rows, with each row having 4 cubes. The box would have a total of 60 cubes.