Here's how you can use the crushed stone calculator: Select your surface shape, e.g., Rectangular.. In surface length, enter the length of your surface, e.g., 12 feet.. In surface width, enter the width of your surface, e.g., 8 feet.. Now, enter in depth, how deep do you want to fill the layout of your surface, e.g., 3 inches.. The waste factor tells how much crushed stone wastes during the ...