Some shipping companies have the option to pay to ship your package by volume instead of weight. This is beneficial because you can fit as much as you are able into the same box and pay a flat rate to have it shipped. If you have a box that you need to calculate volume for shipping, you can do it in a few minutes.
Take a tape measure and measure the height of the box. Write down the exact inches on a piece of paper.
Measure the box's length and width and write down the number from the tape measure in inches.
Multiply the numbers you wrote down in order on the calculator and press the "=" button (i.e., 15 x 20 x 20 = 4500 cubic inches). For cubic feet, divide your final number by 1728, which is one cubic foot (i.e., 4500 / 1728 = 2.6 cubic feet).