Many landscapers and homeowners choose river rock for their outdoor spaces for its variety of colors and smooth shape. River rock comes in many sizes and is used for walkways, driveways, and borders. This type of landscaping rock adds curb appeal and warmth to any landscaping project, and an accurate river rock estimate will help your project stay on budget.
Unlike gravel or crushed stone, river rock has smooth round edges that allow for more air between the stones. River rock sizes vary from ½-inch to over 6 inches, making its calculation different from other gravel landscaping material. Hardscape vendors calculate river rock usage the same way as gravel—by the cubic yard— when the size is up to three inches, and by the ton at sizes over three inches.
Regardless of the size you choose, you will need to calculate the square footage of the area you wish covered with river rock and convert that to cubic yards. If your river rock is larger than three inches, you’ll need to convert your cubic yards to tons. Additionally, river rock measuring over three inches in size lays in a single layer on the covered area.
On This Page:
- How to Calculate River Rock
- Example Calculation
How to Calculate River Rock
Determine the area in square feet by plugging your measurements into this formula:
- The length of your area in feet.
- The width of your area in feet.
- The depth of the stone in feet—divide the depth by 12.
The river rock calculator formula for rock under three inches is as follows:
(Length x width x depth) / 27
This final number is how many cubic yards of material you will need.
Real-World Calculation Example
To put this formula to practical use, follow this example. Imagine that you wish to cover a 10-foot x 10-foot area with 3-inch river rock. Multiply 10 by 10 to reach 100 square feet. Your river rock is three inches tall. Divide three inches by 12 to reach 0.25 feet. Multiply 0.25 by 100 and your volume is 25. Divide 25 by 27 to reach 0.93 cubic yards. River rock weighs about 2,600 pounds or 1.3 tons per cubic yard. In this example, your project would need 1.2 tons of rock.
What if Your Area is a Circle?
Circular areas require a bit more calculation. A circle with height is a cylinder. The volume of a cylinder = (radius x radius) x 3.14 x height in feet.
For a ten-foot circle, your calculator would look like this:
- 10 ÷ 2 = 5
- 5 x 5 = 25
- 25 x 3.14 = 78.5
- 5 x 0.25 (3 inches of pea gravel, in feet) = 19.625
- 19.625 ÷ 27 = 0.72 cubic yards
You can also multiply the length and width of the circle and multiply by 0.8 or 80% to reach an approximate but usable area. In this example, your project would need 0.94 tons of river rock.
Calculating River Rock Coverage by Weight
Larger sizes of rock are trickier to calculate, so once you have your square footage, skip the depth calculation and use the following estimates:
- River rock measuring 3 to 6 inches will cover roughly 50 square feet per ton.
- River rock measuring 6 inches and over will cover roughly 25 square feet per ton.
Accurate measuring saves time and money and helps you stay on budget. For landscaping stone, it’s important to get it right since multiple deliveries and trips back and forth to your vendor are costly and time-consuming.Find River Rock Delivery Pros Near You