# How to Calculate River Rock

River rock comes in several sizes, such as 1 1/2-inch stones or 4-inch stones. The size of stone you choose affects how many bags or tons it takes to cover the area you're landscaping. Smaller stones work well filling in between stepping stones or as flowerbed mulch, while larger stones help with erosion control.

## Measuring the Area

Knowing the size of the area you plan to fill with river rocks helps you accurately calculate how much of the rock you need. For square or rectangular areas, just multiply the length of the space by the width. For example, if your flowerbed is 10 feet long and 6 feet wide, it's 60 square feet.

For circles, measure the radius, which is the distance from the center of the circle to an outer edge. Multiply the radius by itself, then multiply that number by 3.14 to find the square footage. For example, if the radius is 5 feet, multiply 5 by 5 to get 25, then multiply that by 3.14 for 78.5 square feet.

### Tip

Break down odd shapes into smaller circles or squares when possible, then add the square footages together.

## Planning the Depth

How deep you plan to install the river rocks makes a difference in how much you need. 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.

When you divide the cubic feet by 27, you get the number in cubic yards. If you had 120 cubic feet, for example, divide 120 by 27 to get about 4 1/2 cubic yards. If you need the amount in tons, multiply the cubic yards by 1.35.