You cancalculatethe volume of gravel by multiplying area of gravel path by the desired depth: For e.g. 200 ft 2 * 1 ft = 200 ft 3; Purchase enough landscaperockto cover the area. If the area to be covered is 200 cubic feet, for example, each bag ofrockcovers 4 cubic feet ,so you will need 50 bags of landscaperockto fill the space.