Introduction
River rock shows up in dry creek beds, xeriscape front yards, around downspouts, and along foundation edges. It reads as finished hardscape, but the ordering math is the same as any aggregate: area times depth, adjusted for the air gaps between stones. The trick is picking the right void ratio. Rounded river rock packs tighter than crushed gravel. A 25% void ratio is typical, not the 30% you’d use for angular stone.
Size matters for weight, too. Larger river rock has more air between pieces, so the density drops. In this calculator, pea gravel presets to 95 lb/ft³, medium rock to 90, large to 88, and extra-large to 85. That’s why a cubic yard of pea gravel weighs more than a cubic yard of 3 to 5-inch rock even though both are the same material.
Most residential projects use a 2 to 3-inch layer for decorative cover. Dry creek beds go deeper, often 4 to 6 inches, so the stone reads as a streambed rather than a thin veneer. Enter your depth and the calculator handles the rest, including a delivery cost field that works whether your supplier quotes by the load, the ton, or a flat fee.
How to Use the River Rock Calculator
Select your currency from the dropdown if you want the cost output in something other than US dollars.
Enter the bed length and width. Choose feet, inches, yards, meters, centimeters, or millimeters.
Enter the stone depth. Two to three inches covers most decorative beds. Four to six inches suits dry creek beds.
Pick a river rock size from the dropdown. Each preset loads a matching density.
Confirm the density value. Switch to Custom if you want to enter your own, and pick lb/ft³, kg/m³, lb/yd³, or ton/yd³ as the unit.
Set the void ratio. Twenty-five percent is the default for rounded river rock. Drop it to 20% if the stone is very uniform and tightly placed.
Add a waste factor. Ten percent covers spillage and slight over-excavation.
Enter the price per unit weight and pick per ton, per pound, or per kilogram.
Add delivery cost if it isn’t included in the stone price. Choose flat total, per ton, or per load (assumes 20 tons per truck).
Enter fabric or geotextile cost as a total or scaled per square foot or square meter.
Add any labor cost as a lump sum.
Hit Calculate. The Summary tab shows the headline figures. The Detailed Breakdown tab lists every intermediate value.
How the River Rock Calculator Formula Works
Everything converts to feet and pounds internally before the tool runs the numbers.
Formula: Surface Area (ft²) = Length (ft) × Width (ft)
Formula: Solid Volume (ft³) = Length × Width × Depth (ft)
Formula: Volume with Voids (ft³) = Solid Volume ÷ (1 − Void % ÷ 100)
Formula: Volume with Waste (ft³) = Volume with Voids × (1 + Waste % ÷ 100)
Formula: Weight (lbs) = Solid Volume × (1 + Waste % ÷ 100) × Density (lb/ft³)
Formula: Weight (tons) = Weight (lbs) ÷ 2000
Formula: Rock Cost = Weight (lbs) × Price per lb
Formula: Total Cost = Rock Cost + Delivery + Fabric + Labor
Two things trip people up. First, the void ratio changes the volume you need, not the weight. Air doesn’t weigh anything, so the tonnage comes from solid volume times density. Second, the size presets drive density. A yard of pea gravel is heavier than a yard of 3 to 5-inch rock because the small stones pack more material into the same space.
Delivery supports three modes. A flat total adds a fixed dollar amount. A per-ton rate multiplies by total tonnage. A per-load rate divides by 20 tons and rounds up, which assumes a standard dump truck load. If your supplier uses a different truck size, switch to a flat total and enter the number they quote.
Fabric cost is worth including if you’re laying geotextile under the stone. It stops soil from migrating into the rock layer and keeps the bed draining. Enter a per-square-foot rate and the calculator multiplies it by surface area. Same for per-square-meter, which uses a 0.092903 conversion.
Worked Example
You’re covering a 24 ft by 6 ft side yard with small river rock at 2.5 inches deep. The stone runs $58 per ton from a local landscape supplier, with delivery as a flat $95 fee. You’re adding 10% waste and using a 25% void ratio. No fabric, no labor.
Step 1: Convert depth to feet.
2.5 inches ÷ 12 = 0.2083 ft.
Step 2: Surface area.
24 × 6 = 144 ft².
Step 3: Solid volume.
24 × 6 × 0.2083 = 30.0 ft³.
Step 4: Apply the void ratio.
30 ÷ (1 − 0.25) = 30 ÷ 0.75 = 40.0 ft³.
Step 5: Add 10% waste.
40 × 1.10 = 44.0 ft³.
In cubic yards: 44 ÷ 27 = 1.63 yd³.
Step 6: Calculate weight.
30 × 1.10 × 95 = 3,135 lbs.
In tons: 3,135 ÷ 2000 = 1.57 tons.
In kilograms: 3,135 × 0.453592 = 1,422 kg.
Step 7: Rock cost.
1.57 × $58 = $91.06.
Step 8: Total cost with delivery.
$91.06 + $95.00 = $186.06.
The Summary tab reads 144 ft² of surface area, 30 ft³ solid volume, 44 ft³ with voids and waste (1.63 yd³), 1.57 tons of stone, and $186.06 total. The breakdown tab walks through each conversion.
Switch the size to extra-large rock and the density drops from 95 to 85 lb/ft³. That same area now weighs 2,805 lbs, or 1.40 tons about 11% lighter. The volume stays the same, but the invoice drops.
