ROCK
How much does a yard of rock cover?
One cubic yard of rock covers 324 square feet at 1 inch deep. Divide 324 by the depth in inches and you have the coverage at any depth — the same relationship every bulk material on this site runs on, because a cubic yard is 27 cubic feet whether it holds stone, mulch or compost.
The table
| Depth | Square feet covered | How many yards for 400 sq ft |
|---|---|---|
| 1 inch | 324 | 1.23 |
| 2 inches | 162 | 2.47 |
| 3 inches | 108 | 3.70 |
| 4 inches | 81 | 4.94 |
| 6 inches | 54 | 7.41 |
Both columns are arithmetic. Coverage is 324 ÷ depth; the yardage is 400 × depth ÷ 324. The second column is there because the coverage figure is the one people quote and the yardage is the one they order — and going from "a yard covers 324 sq ft" to "I need 3.70 yards" is where the mistake usually happens.
An independent published version of the coverage relationship, stated for compost by a university extension service, is on the cubic yard calculator page with its source and the date it was read.
Why "a yard of rock" may not be what you are being sold
Decorative and crushed stone are frequently priced and delivered by weight, not by volume. That means the quote you receive may be in tons, and a ton is not a yard — how many square feet a ton covers depends on how much a cubic yard of that particular stone weighs, which varies by rock type, by gradation and with moisture.
So the sequence matters: work out your volume in cubic yards first, from the table above, and only then deal with the supplier's unit. If they quote tons, ask for their pounds per cubic yard for that product, or ask them to re-quote in cubic yards.
Worked example
A 400 sq ft bed at 2 inches: 400 × 2 ÷ 324 = 2.47 cubic yards. At 2 inches a cubic yard covers 162 sq ft, and 400 ÷ 162 = 2.47 — the same number by the other route.
If the supplier's minimum load is 3 cubic yards, that is the order. If they sell half yards, 2.5 yards leaves you about 5 sq ft short of the full bed at that depth; decide whether the shortfall is acceptable or whether the extra half yard is cheaper than a second delivery.
What the coverage figure does not include
- Waste. Rock is fitted around obstacles and cut at edging. Add your allowance to the total, once, at the end.
- Settlement. Rounded stone settles into the surface beneath it more than angular stone does, so a shallow dressing can end up thinner than planned.
- The membrane. It does not change the volume, but if it is not down first, the coverage you calculated is not the coverage you get.
Related calculators
How much landscape rock do I need for the measuring version · Landscape rock calculator · River rock calculator for smooth rounded stone · How much does a yard of mulch cover for the same table on a lighter material.
The arithmetic is from the definitions 1 cubic yard = 27 cubic feet and 1 foot = 12 inches. No density figure is published here, because density is specific to the stone being sold.