Adding river rock or gravel is one of the best ways to reduce garden maintenance, improve drainage, and give your flower beds a clean, professional finish. However, the biggest hurdle for any DIY landscaper is the math. Unlike mulch, which is light and forgiving, landscape rock is sold by the ton or the cubic yard. If you under-order, you face expensive second-delivery fees. If you over-order, you’re left with a literal ton of stone sitting on your driveway.
Use our Landscape Rock Calculator to determine exactly how much material you need. Our tool is unique because it factors in the density of your specific rock typeβbecause a cubic yard of Lava Rock weighs significantly less than a cubic yard of River Stone.
Landscape Rock Calculator
How to Use the River Rock Calculator
- Area (sq ft): Enter the total square footage of the space you want to cover. (Length Γ Width).
- Depth (inches): For most applications, 2 to 4 inches is the standard. If you are using a weed barrier, 3 inches is the “Goldilocks” depth for total coverage.
- Rock Type: Select the material you are using. This is crucial for weight estimation, as materials like Lava Rock are much more porous and lighter than dense River Rock.
Why We Built This: The “Secret Sauce” of Rock Density
The “Secret Sauce” of our tool is the Density Selector. Most basic calculators assume 1 cubic yard equals 1.35 tons. While this is true for standard gravel, it is wildly incorrect for Lava Rock (0.8 tons/cy) or Decomposed Granite (1.45 tons/cy).
By selecting your specific material, our tool adjusts the tonnage requirement, preventing you from overpaying for weight you don’t need or under-ordering for dense materials.
Educational Guide: Choosing and Installing Landscape Rock
Landscape rock serves two primary purposes: aesthetics and weed suppression. To ensure your investment lasts for years, follow these professional installation tips.
The Importance of Weed Barriers
Never lay rock directly on top of soil. Over time, the heavy stones will sink into the dirt, allowing weeds to grow through the gaps. Always install a high-quality, woven landscape fabric first. This allows water to drain into the soil while keeping your rocks clean and on the surface.
Sizing Your Rock
- Pea Gravel (1/4″ – 1/2″): Excellent for pathways and around fire pits. It is easy to walk on but can be easily displaced by leaf blowers.
- River Rock (1″ – 3″): Best for flower beds and drainage swales. It stays in place well and provides a natural, “dry creek bed” look.
- Lava Rock: Extremely lightweight and great for retaining moisture in the soil, but its jagged edges make it difficult to walk on and harder to clean.
Calculating for Irregular Shapes
If your garden bed is a circle, calculate the area as Ο Γ rΒ². If itβs an oval, use Length Γ Width Γ 0.8. Adding a 5-10% “waste factor” is always recommended to account for settling and uneven sub-surfaces.
Frequently Asked Questions
Q: How many bags of rock are in a cubic yard?
A: Standard landscape rock bags found at big-box stores are usually 0.5 cubic feet. There are 27 cubic feet in a cubic yard, so it takes 54 bags to equal one cubic yard.
Q: How deep should river rock be?
A: We recommend a depth of 3 inches. This is deep enough to hide the underlying landscape fabric and prevent sunlight from reaching weed seeds, but not so deep that it becomes a drainage issue or a waste of money.
Q: Will river rock help with drainage?
A: Yes! Rock is an excellent material for “French Drains” or dry creek beds. Unlike mulch, which can wash away in heavy rain, rock stays in place and allows water to flow freely between the stones.
