River Rock Calculator
Decorative river rock yards and tons by area and depth
What is river rock calculator?
A river rock calculator answers the landscaper’s two questions on any decorative install: how many cubic yards do I need, and how does that map to tons for the supplier quote. The volume math (area times depth) is straightforward; landscape supply yards quote in tons, and density varies a bit by stone size and grade.
The default density is 95 lb/ft³, typical for general river-tumbled rock — the smooth round shape leaves more air space between stones than crushed angular stone, which is why the density is at the lower end of decorative stones. Smaller pebble grade is a touch denser; larger 3-5 inch stone is lighter because of more void space.
What depth to choose? Two inches works for refreshing existing river-rock beds. Three inches is the textbook minimum for first-time install over fresh weed barrier — anything thinner won’t hide the fabric or suppress germinating weeds. Four to six inches is right for dry creek bed features, where you want stones to look naturally piled, and for any bed using larger 1.5-inch-and-up rock.
Bulk vs bagged: river rock is rarely sold in retail bag sizes for any project past a single planter. Landscape supply yards sell by the ton, typically $50-120 per ton delivered depending on color (gray basalt is cheap; tumbled Mexican beach pebble is premium). Bulk wins on price for any bed past a few square feet.
The 10% waste factor default covers spread loss and minor over-fill at edges. Bump to 15% for organic shapes — curved beds and dry creek features always burn through the overage faster than blocky rectangles. For mixed-size rock, void space between irregular stones reduces effective coverage; 15% is the safer choice there too.
Always lay heavy-duty landscape fabric beneath river rock. Without it, stones sink into soil within a season or two, and weeds grow up between them. The extra hour of install pays back in a decade of low-maintenance coverage.
When to use a river rock calculator
- Naturalistic decorative bed — Replace mulch with river rock for a permanent, no-maintenance bed cover. 2-3 inches over weed barrier hides the fabric.
- Dry creek bed feature — Mixed-size river rock simulates a stream bed. The calculator handles average depth across the cross-section of the bed.
- Walkway edging — River rock borders along beds, paths, or driveways. Output in tons matches landscape supply pricing.
How to use the River Rock Calculator
- Measure the area — For rectangular beds and borders, multiply length by width. For curved or organic shapes (dry creek beds), break the area into segments and sum, or use average width times length.
- Pick a depth — Use 2-3 inches for decorative beds (3 inches if the rock is 1.5 inches and up). Dry creek beds need 4-6 inches for the most natural appearance and to fully hide the fabric layer.
- Read the tonnage — Bulk river rock is sold by weight at landscape supply yards. Output shows tons (1 cu yd of river rock weighs roughly 1.28 tons at the default density).
- Apply waste factor — 10% covers spread loss and minor over-fill. Bump to 15% for organic shapes or mixed-size rock — void space between irregular stones eats into effective coverage.
Worked examples
Front yard bed, 200 ft^2 at 3 in
Input: 10 ft x 20 ft x 3 in depth
Output: 1.85 cu yd / 2.64 tons (with 10% waste)Dry creek bed, 3 ft x 30 ft
Input: 3 ft x 30 ft x 5 in depth
Output: 1.39 cu yd / 1.98 tonsUse mixed sizes — 1 in to 4 in range — for the most natural look.
Border strip, 18 in x 60 ft at 2 in
Input: 1.5 ft x 60 ft x 2 in depth
Output: 0.56 cu yd / 0.79 tons