Calculate the amount of gravel needed for a project by multiplying the length by the width and then the depth of the area. If all measurements are in feet, divide the answer by 27 to convert from cubic feet to cubic yards, the measurement most suppliers use when selling gravel.
Most new projects require approximately 4 inches of gravel, according to Billie Jo Jannen for SFGate. If this is the desired thickness, use one-third foot as the thickness of the gravel. Sometimes gravel is sold by the ton instead of by the cubic yard. If buying by the ton, ask the supplier the number of cubic feet per ton and divide the cubic feet from the calculation by this number to determine the number of tons the project requires.