River Rock Calculator

Area in square feet, times depth in feet, divided by 27. That gives cubic yards. Multiply by 1.35 for US tons.

A 20 by 10 ft bed at 3 inches deep is 50 cubic feet of stone, 55 once you add 10 percent for waste, which is 2.04 cubic yards or 2.75 tons. The calculator above does this for any shape, including circles and L-shapes.

This is where calculators quietly disagree, and river rock is worse than pea gravel for it, because the weight depends on the stone size. Bigger stones leave bigger gaps, so a cubic yard of large rock holds less stone and weighs less.

Published figures across suppliers and calculators run from about 2,400 to 3,000 pounds per cubic yard. This site uses 2,700 pounds, or 1.35 tons, the middle of that range, and says so on every page.

On a 3 cubic yard order the spread between 1.20 and 1.50 tons per yard is nearly a ton of material. If you are buying by weight, ask the yard what their stone weighs. The full set of figures is published as open data.

The depth rule is about twice the largest stone. Lay 1 to 3 inch rock at 3 inches and it covers the ground properly. Lay it at 1 inch and you can see soil between the stones, which is where weeds start.

That rule is also why bigger stone costs more per square foot than the price per ton suggests. Doubling the stone size roughly doubles the depth you need, which doubles the tonnage.

These are arithmetic figures at our density. In practice large stone covers less than the table says, because the gaps between pieces waste depth. For 3 inch rock and above, take 10 to 15 percent off the coverage and add it to your order.

Suppliers often quote one ton as covering 100 square feet at 2 inches. That implies a heavier stone than we assume, around 3,240 lb per cubic yard. Neither figure is wrong, they are different assumptions, which is the whole reason this site publishes its own.

The choice is rarely about price. River rock is for water and for looks, pea gravel is for surfaces people walk on, and crushed stone is for anything that carries weight.

If you are weighing river rock against pea gravel for a path, the pea gravel calculator covers depth and base. For driveways, neither rounded stone works well, which the driveway guide explains.

It works well for

• Dry creek beds. The large voids move water fast and the rounded stone looks like it belongs in a watercourse.
• Downspout splash zones and drainage runs. Stone big enough not to wash away when the roof empties onto it.
• Beds and borders. It does not break down the way bark does, so it is laid once rather than topped up yearly.
• Erosion control on banks, in the 3 to 5 inch sizes, where smaller stone would simply wash down.
• Xeriscape and low water planting, where the stone is the ground cover rather than a mulch.

It is the wrong choice for

• Paths and patios. Rounded stone above an inch rolls underfoot. Guests notice within one step.
• Anything on wheels. Wheelbarrows, strollers and wheelchairs all sink and drag.
• Play areas. Too large to cushion a fall and easy to throw.
• Driveways. Rounded stone will not lock together under tyres, so it ruts and migrates.
• Right against a house wall, where large stone can trap debris and hold moisture against the siding.

River rock costs $45 to $130 per US ton delivered, which is roughly $60 to $175 per cubic yard at our density. That is two to three times the price of pea gravel, and the spread inside the range comes down to colour, size and how far it travelled.

Delivery adds about $10 to $25 per ton, or $5 to $10 per mile where a yard charges by distance. Bagged river rock exists but is rarely sensible past a few bags, for the same reason it is not sensible with pea gravel.

The cost guide covers delivery, minimum loads and the bulk against bagged crossover in detail. The same logic applies to river rock, at a higher price per ton.