How do I calculate how much stone I need?

Multiply length by width by depth with everything in feet to get cubic feet, multiply by the stone's density in pounds per cubic foot, then divide by 2,000 for tons. A 20 ft × 10 ft bed at 3 inches of river rock is 50 × 105 ÷ 2000 = 2.63 tons.

How many tons of rock are in a cubic yard?

Between 1.2 and 1.5 tons for most crushed stone and river rock, because a cubic yard holds 27 cubic feet and typical stone runs 95 to 110 pounds per cubic foot. Lava rock is the outlier at roughly 0.7 tons per cubic yard — it is less than half the weight for the same volume.

How much area does a ton of stone cover?

About 120 square feet at 2 inches deep, 80 sq ft at 3 inches and 60 sq ft at 4 inches, for stone around 100 lb/cu ft. Lighter stone covers more ground per ton: a ton of lava rock spreads over roughly 160 sq ft at 3 inches.

How deep should landscape stone be?

Two inches for decorative beds you walk around, 3 inches where you want weed suppression, and 4 inches for paths and high-traffic areas. Going deeper than 4 inches on a bed wastes material and makes planting awkward without improving anything.

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

Bulk, once you pass roughly half a cubic yard. Bagged stone typically costs three to five times as much per cubic foot, though it wins for small beds, for jobs a truck cannot reach, and when you have nowhere to dump a pile.

What is the difference between stone, rock and gravel?

In supplier terms they overlap heavily. Gravel usually means smaller graded material used as a base or driveway surface; landscape stone and rock cover the decorative sizes — river rock, marble chips, lava rock. The calculation is identical, only the density changes.

Should I order extra stone?

Add about 10 percent. Beds are rarely the clean rectangle you measured, stone settles into the soil at the edges, and the last barrow always comes up thin. For a bulk delivery it costs little to round up to the next half yard.

Stone Calculator: Tons of Landscape Rock Needed

Landscape stone is sold by weight, spread by depth and measured by area, and the number that connects those — density — swings more than people expect. River rock and lava rock look like similar quantities in the yard, but a cubic yard of one weighs twice what the other does. Order by volume and you might be fine; order by tonnage using the wrong density and you will be well out.

Stone Calculator formula — The Stone formula

The stone tonnage formula

and are the bed’s length and width in feet, is the depth in inches, is the stone’s loose density in pounds per cubic foot, and 2,000 is the number of pounds in a US short ton.

If your supplier sells by volume rather than weight, stop after the first three terms and divide by 27:

That figure does not depend on density at all, which is why volume is the safer unit to order in when you are not certain what the material weighs.

Worked example

A 20 ft by 10 ft bed, filled with river rock to a depth of 3 inches.

Step 1 — convert the depth to feet.

Step 2 — volume in cubic feet.

Step 3 — multiply by river rock’s density.

Step 4 — convert to tons.

That is 1.85 cubic yards, or 100 of the half-cubic-foot bags sold at garden centres — which is the moment bulk delivery stops being optional and starts being obvious.

Swap river rock for lava rock and the same bed needs tons. Same volume, less than half the weight, and usually a very different price per ton.

Stone Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

Stone density reference

Stone	lb per cu ft	Tons per cu yd
Lava rock	50	0.68
Sandstone / flagstone chips	85	1.15
Crushed limestone	95	1.28
Pea gravel	96	1.30
Crushed stone (#57)	100	1.35
Marble chips	101	1.36
River rock, rounded	105	1.42
Decomposed granite	110	1.49

These are loose densities, which is what a delivered pile actually weighs. Compacted figures run 10 to 20 percent higher and are the right ones for a driveway base, not a decorative bed. The tons-per-cubic-yard column is just the middle column times 27 divided by 2,000, and it is the number most suppliers quote from.

Coverage per ton

For stone around 100 lb/cu ft:

Depth	One ton covers
1 in	240 sq ft
2 in	120 sq ft
3 in	80 sq ft
4 in	60 sq ft
6 in	40 sq ft

The rough field rule for 100 lb stone is 240 divided by the depth in inches. For lava rock at 50 lb/cu ft, double it. For decomposed granite at 110, knock off about 10 percent.

How deep to spread it

Use	Depth
Decorative bed, planted	2 in
Decorative bed, weed suppression	3 in
Walking path	3–4 in
Dry creek bed / drainage	4–6 in
Driveway surface course	3–4 in over a compacted base

Two inches is genuinely enough for a bed you are only looking at. Three is the number worth paying for if weeds are the reason you are laying stone, because that is roughly where light stops reaching seed at the soil surface. Beyond four inches on a bed you are buying depth nobody will ever see.

Landscape fabric underneath is worth the cost on a decorative bed and actively counterproductive on a path, where it eventually surfaces in ripples. Either way it does not change the volume you need.

Bags versus bulk

Half-cubic-foot bags are the standard retail size, so a cubic yard is 54 of them. The worked example above needs 100 bags, which is two pallets and a lot of carrying.

Volume needed	Sensible way to buy
Under 0.25 cu yd (about 14 bags)	bags
0.25 to 0.5 cu yd	bags, unless delivery is cheap
Over 0.5 cu yd	bulk, delivered
Over 3 cu yd	bulk, and expect a better per-ton rate

Bagged stone usually costs three to five times as much per cubic foot as bulk. The break-even is not really about the material price though — it is about whether a truck can get to where the stone needs to end up, and whether you have somewhere to put a pile for a weekend.

What changes the answer most

Density. The single largest lever. Getting it wrong by picking “stone” generically instead of the actual material can be a factor of two on lava rock.

Depth. Multiplies straight through. Going from 2 to 3 inches is 50 percent more stone, not a small adjustment.

Shape. Beds are curved. Measure the bounding rectangle for ordering and accept a small over-estimate, or split a complex bed into rectangles with the square footage calculator first.

Settlement. Stone works into soft soil over the first season, especially without fabric. That is most of why the 10 percent margin exists.

Common mistakes

Using one density for every stone. Lava rock at 50 lb/cu ft and decomposed granite at 110 are more than twice apart.
Leaving depth in inches inside the multiplication. Divide by 12 first.
Using compacted density for a decorative bed. Loose is what gets delivered and what fills the bed.
Ordering tons when the quote was in yards. Confirm which unit the supplier means before agreeing a number — they are not interchangeable and the ratio depends on the material.
Measuring a curved bed as its outline. You will over-order. Break it into rectangles instead.
Forgetting edging. Stone spreads sideways without a border, and a bed with no edge needs topping up every year.

For driveway base and graded gravel rather than decorative stone, the gravel calculator handles metric units and gravel-specific densities. For bark and wood chips, the mulch calculator works the same way with a much lighter material.

About the formula: Tons = (Length × Width × Depth ÷ 12) × Density ÷ 2000, with length and width in feet and depth in inches. Density is the stone's loose unit weight in pounds per cubic foot.

Stone Calculator