River Rock Calculator

How to Calculate River Rock

A simple, step-by-step method to work out exactly how much river rock you need — in cubic yards, tons, and bags. Or skip the math and use the river rock calculator.

Calculating river rock comes down to three things: the area you want to cover, the depth of stone, and the density of the rock. Once you have those, a little arithmetic converts your project into the units suppliers actually sell in — cubic yards for bulk, tons for delivery, or bags for smaller jobs. Here is the whole method.

Step-by-step

  1. Step 1: Measure the area

    Measure the length and width of the space in feet and multiply them to get the area in square feet. For circles, use π × radius². For odd shapes, split the space into rectangles and circles and add the areas together.

  2. Step 2: Choose a depth

    Pick how deep the river rock should be, in inches. Use about 2 inches for small decorative stone and 3–4 inches for larger 1–3" or 3–5" rock so the ground does not show through.

  3. Step 3: Find the volume in cubic feet

    Multiply the area in square feet by the depth in feet (depth in inches ÷ 12). This gives the volume of river rock you need in cubic feet.

  4. Step 4: Add an overage allowance

    Add about 10% to your volume for settling, uneven ground, and waste. Multiply your cubic feet by 1.10.

  5. Step 5: Convert to cubic yards, tons, or bags

    Divide cubic feet by 27 for cubic yards. Multiply cubic feet by about 100 lb/ft³ and divide by 2,000 for tons. Divide cubic feet by the bag size (e.g. 0.5 ft³) for the number of bags.

The river rock formula

If you prefer it as one expression:

Cubic feet = Area (ft²) × (Depth in inches ÷ 12) × (1 + waste)
Cubic yards = Cubic feet ÷ 27
Tons = Cubic feet × density (≈100 lb/ft³) ÷ 2,000
Bags = Cubic feet ÷ bag size (e.g. 0.5 ft³)

River rock weighs roughly 1.3–1.4 tons per cubic yard, though it varies by stone size and type. We document the density values we use on the methodology page.

Worked example

Suppose you're covering a 20 ft × 15 ft bed — that's 300 square feet — with 2 inches of river rock.

At that size, bulk delivery is far cheaper than 110 bags — see river rock cost for the bags-vs-bulk break-even.

Calculating an irregular shape

Real yards are rarely a perfect rectangle. The reliable approach is to break the area into simple shapes — rectangles, circles, triangles — find each area on its own, then add them together. For a ring of rock around a tree or pool, subtract the inner circle from the outer circle: Area = π × (outer radius² − inner radius²). The calculator's multi-area and ring modes handle both automatically.

Coverage reference

If you already know your area and just want a quick read on quantity, this chart shows how far one ton or cubic yard of river rock goes at common depths.

DepthSq ft per tonSq ft per cubic yard
1" 240 324
2" 120 162
3" 80 108
4" 60 81

Frequently asked questions

How do I calculate how much river rock I need?

Multiply the area in square feet by the depth in feet (depth in inches ÷ 12) to get cubic feet. Divide by 27 for cubic yards, or multiply cubic feet by about 100 lb/ft³ and divide by 2,000 for tons. Add 10% for waste.

How do you calculate cubic yards of river rock?

Find the volume in cubic feet (area × depth in feet), then divide by 27. For example, 300 sq ft at 2 inches deep is 50 cubic feet, which is about 1.85 cubic yards before overage.

How much area does a yard of river rock cover?

One cubic yard of river rock covers about 162 square feet at 2 inches deep, 108 square feet at 3 inches, and 324 square feet at a 1-inch depth.

How do I calculate river rock for an irregular shape?

Split the area into simple shapes — rectangles, circles, and triangles — calculate each one separately, then add the results together. The calculator’s multi-area mode does this for you.

Skip the arithmetic. Enter your measurements and get cubic yards, tons, bags, and cost instantly.

Open the River Rock Calculator →

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