Small rocks or gravel are popular options for surfacing accent borders and other areas in landscaping projects. Rocks can create an attractive appearance and serve the practical purpose of holding soil in place when grass or other ground cover isn’t the best choice. It is best to allow a little extra when you figure out the amount of rocks you'll need. You don’t want to run short and any excess will probably come in handy for another project soon enough.
Determine the total square footage of rocks needed. Measure the length and width of each area to be covered and then multiply length times width to find the square footage. Add up the square feet for each section of your project to get the total number of square feet.
Decide on the depth of rock cover you need. This can vary depending on the size of rocks or gravel and the type of area you want to cover. In general, you’ll want a depth of around 3 to 4 inches.
Convert the depth in inches into a decimal fraction of one foot by dividing the depth by 12. For example, a 3 inch layer of rock divided by 12 equals 0.25 feet. Multiply by the number of square feet to determine the number of cubic feet required.
Convert cubic feet to cubic yards by dividing by 27 (the number of cubic feet in one cubic yard). For instance, if you need 135 cubic feet of rocks, dividing 135 cubic feet by 27 gives you 5 cubic yards.
Convert cubic yards to tons of rock. For most gravel and small rock, there are about 1 and 3/8 tons (2750 pounds) per cubic yard. Multiply the number of cubic yards by 1 and 3/8. For 5 cubic yards, this works out as 1 and 3/8x5 = 6 and 7/8 tons.