How is river rock different from gravel?

River rock is naturally rounded and smooth from years of water tumbling, while gravel is usually crushed stone with angular edges. They're often interchangeable for decorative ground cover, but river rock's larger, smoother pieces suit accent beds and dry creek features, while gravel suits paths and sub-bases better.

How deep should a river rock bed be?

5-7.5 cm (2-3 in) suits small decorative rock as ground cover; larger cobbles or a drainage bed need 10-15 cm (4-6 in) so the rock forms a proper layer rather than a thin scatter over visible soil.

Is it cheaper to buy river rock in bulk or by the bag?

Buying by the cubic yard from a landscaping supplier or quarry is almost always cheaper per unit than buying bagged river rock from a hardware store, which typically runs several times the bulk price -- bags only make sense for very small accent areas or top-ups.

River Rock Calculator | Decorative Stone Coverage, Weight & Cost

How much river rock do you need?

River rock -- smooth, water-rounded stone -- is a popular choice for garden borders, dry creek beds, and decorative ground cover where sharp gravel would look out of place. Ordering it by guesswork usually means a second delivery or a leftover pile taking up space. This calculator works out the volume, weight, and cost of river rock for a bed, path, or drainage area from the length, width, and depth you enter, plus your chosen rock type and a waste allowance for spillage and settling.

How to use the river rock calculator

Enter the length and width of the area you're covering.
Enter the depth of the rock layer -- typically 5-7.5 cm (2-3 in) for decorative ground cover, or 10-15 cm (4-6 in) for a drainage bed.
Pick a rock type from the dropdown (standard river rock, pea gravel, crushed granite, quartzite, or crushed asphalt) and adjust the waste allowance if needed, then read off the volume, weight, and estimated cost.

The river rock calculation, step by step

Volume = Length x Width x Depth. Add a waste allowance for spillage and settling before converting to weight: Order volume = Volume x (1 + waste%).

Weight = Order volume x the rock's bulk density. Standard river rock runs around 1,425 kg/m3 -- denser than light pea gravel, but lighter than crushed granite or quartzite (see the calculator's material dropdown for exact figures per type).

Worked example: a 5 m x 2 m bed, 7.5 cm (0.075 m) deep, standard river rock, 10% waste allowance. Volume = 5 x 2 x 0.075 = 0.75 m3. With waste: 0.75 x 1.1 = 0.825 m3, about 1.08 cubic yards. Weight = 0.825 x 1,425 = 1,176 kg, roughly 1.18 tonnes.

Pro tips

At a typical US price of around $200 per cubic yard, a 5 m x 2 m (about 16 ft x 6.5 ft) bed at 7.5 cm (3 in) depth -- roughly 1.08 cubic yards including a 10% waste allowance -- of standard river rock would cost about $216 in material, before delivery.

Match bed depth to rock size. Small, pea-gravel-sized river rock covers well at 5 cm, but larger 5-10 cm cobbles need at least a 10 cm bed depth to look intentional rather than sparse.
Lay landscape fabric underneath before spreading. It stops rock sinking into the soil and keeps weeds from pushing up through the gaps -- skipping it is the most common reason a river rock bed looks patchy within a year.