### How to Calculate River Rock | Hunker

This number helps you determine the number of cubic feet or cubic yards of rock required. To find this number, decide how deep you want the rocks to be, such as 2 inches. Convert the inches into feet by dividing 2 by 12 to get 0.167. Multiply the square footage by the depth, such as 60 times 0.167 for about 10 cubic feet.