Rock Calculator

Use this rock calculator to work out how much landscape rock to order: river rock, pea gravel, crushed stone or decorative rock. Enter the size and depth of each area and it gives you cubic yards and tons. Rock is sold by weight, and the weight of a cubic yard changes from one rock and one supplier to the next. So the tons come as a range built from published figures, and one supplier number turns it into a single answer.

About the rock calculator

Working out the volume of rock is simple geometry. The hard part is the step most tools hide: turning cubic yards into tons. We checked the weights that suppliers and other calculators publish, and for river rock alone they run from 1.1 to 1.75 tons per cubic yard. A tool that picks one of those and prints “2.4 tons” is guessing on your behalf.

• Tons as a range. Each rock type carries the lowest and highest published weight. You see both ends and the middle.
• One number when you have one. Type the tons per cubic yard your supplier quotes and the range collapses to an exact figure.
• Several areas in one order. Up to 20 rows, each with its own rock, shape and depth. A river rock border and a crushed stone path go in one estimate.
• Five shapes. Rectangle, circle, triangle, ring, or an area you already know.
• Bags, cost and metric. A bag count for small jobs, a price per ton or per cubic yard, and metric tonnes beside US tons.

It runs in your browser. Nothing you enter is sent anywhere or saved.

How to use the rock calculator

1. Choose your units. Feet with depth in inches, or metres with depth in centimetres.
2. Pick the rock type for the first area. Choose “Other” if your supplier has given you a weight per cubic yard.
3. Pick the shape and enter the measurements and the depth of rock you want.
4. Add more areas if you have them. Use “How many” for identical areas.
5. Add extras. A waste percentage, a bag size, and a price are all optional.
6. Read the result. The headline is tons. Cubic yards, tonnes, bags and cost sit below it.

The rock calculator formula

There are two steps.

1. Volume: cubic yards = square feet x depth in inches / 324

A cubic yard is 27 cubic feet, and there are 12 inches in a foot, so 27 x 12 = 324. For a rectangle, square feet is length times width. For a circle it is 3.1416 times half the diameter, squared.

2. Weight: tons = cubic yards x tons per cubic yard

The second number is the one that varies. The rock calculator runs the sum twice, once with the lightest published weight and once with the heaviest.

How much a cubic yard of rock weighs

These are the figures behind each rock type, in US tons (2,000 lb) per cubic yard, checked on October 2, 2026.

Why do they differ? Three reasons.

• The stone itself. Granite, limestone and sandstone have different densities, and lava rock is far lighter than any of them.
• The size and shape. Round stones leave more air between them than angular crushed stone that locks together. Mixed sizes pack tighter than one size.
• Water. Rock delivered wet weighs more, and you pay for the water if it’s sold by the ton.

None of these figures is wrong. Each describes one supplier’s product. That’s why the only number that settles it is the one from the yard you’re buying from.

Measuring the area

The estimate is only as good as the tape measure. A few habits help:

• Split odd shapes. An L-shaped bed is two rectangles. A bed with a rounded end is a rectangle plus half a circle. Add a row for each piece.
• Use the ring shape for borders. Rock around a tree or a fire pit is a ring: measure across the outside and across the inside.
• Turn inches into decimals. 10 ft 6 in is 10.5 ft. Divide the inches by 12.
• Leave out what you won’t cover. Stepping stones, planters and the trunk of a tree all take up space the rock doesn’t fill.
• Check the depth in a few spots. If the ground dips, use the average.

If you already have the square footage from a plan or a mapping app, choose “I know the area” and type it in.

Rock calculator example: a river rock bed

A bed is 10 ft by 10 ft and you want 3 inches of river rock.

1. Area: 10 x 10 = 100 square feet.
2. Volume: 100 x 3 / 324 = 0.93 cubic yards.
3. Lightest weight: 0.93 x 1.1 = 1.02 tons.
4. Heaviest weight: 0.93 x 1.75 = 1.62 tons.

So the answer is 1.02 to 1.62 tons, with 1.32 in the middle. Here’s the same bed in each rock type:

Example: three areas, three rocks

A front yard has a river rock border, a round pea gravel seating area and a crushed stone path. You add 10% for waste.

At $65 a ton, that’s $514.77 to $669.08 before delivery. The spread is more than two tons, which is the point: you’d want each supplier figure before you place an order this size.

Example: with a supplier’s figure

A gravel driveway is 40 ft by 12 ft at 4 inches deep: 480 x 4 / 324 = 5.93 cubic yards. The quarry says their driveway gravel weighs 1.4 tons per cubic yard. Choose “Other”, enter 1.4, and the rock calculator gives exactly 8.30 tons. At $45 a ton that’s $373.33.

How much one ton of rock covers

Coverage is the formula turned around: 324 divided by the depth in inches, divided by the tons per cubic yard.

The 1.35 column matches the coverage chart Bedrock Landscaping Materials publishes for its rock: 240, 120, 80, 60 and 40 square feet per ton.

How deep to lay rock

• Decorative beds: 2 to 4 inches is the usual range. Stone Center of Ohio suggests at least 2 inches for pea gravel and river rock.
• Paths and driveways: a base of 4 to 6 inches of crushed stone is a common recommendation under pavers, walkways and driveways.
• Drainage: French drains and retaining wall backfill run much deeper, often 8 to 12 inches of washed gravel. Follow the plan for the job.

One rule comes from geometry, not from a supplier: the layer has to be at least as deep as the stones are big. You can’t spread 3-inch stones 2 inches deep. For full coverage with no ground showing through, plan on a layer a bit deeper than the largest stone.

Large rock is different

Depth-based maths works for rock you can rake. For cobbles and bigger stones laid one layer thick, suppliers quote coverage per ton instead. Bedrock Landscaping Materials, for example, lists about 60 square feet per ton for 2 to 4 inch rock and 40 square feet per ton for 4 to 8 inch rock. For stone that size, ask your supplier for their coverage figure and divide your square footage by it.

Tons or cubic yards?

Suppliers sell one way or the other, and it changes which number matters.

• Sold by the cubic yard: use the volume. Weight only matters for the truck.
• Sold by the ton: you need the conversion. Ask “how many tons to a yard for this product?” and enter it under “Other”.
• Sold in bags: bagged rock is usually 0.5 cubic feet. It takes 54 of those to make a cubic yard, so bags suit small jobs only.

If a quote is per ton and another is per yard, set the price unit in the rock calculator to compare them on the same job.

Reading your result

• Tons. The range to plan with, or one number if every area uses a supplier figure.
• The middle. Halfway between the two ends. It’s a reasonable figure for a first budget, not for the final order.
• Cubic yards. Exact, because it’s pure geometry. It includes your waste percentage.
• Metric tonnes. One US ton is 0.907 tonnes.
• Area by area. Shows which area drives the total, and catches typing mistakes.

When the range is wide, order toward the top if a second delivery would cost more than a little spare rock. Order toward the bottom if you can easily collect a top-up yourself.

How much extra to add

Ground isn’t level, edges aren’t straight, and rock settles into soft soil. Stone Center of Ohio builds a standard 10% into its own calculator. Bedrock Landscaping Materials recommends adding 10% by weight for road base and similar material that gets compacted. If you lay landscape fabric on firm ground, you’ll need less. On loose or uneven soil, you’ll need more.

Working in metres

Switch the units and the rock calculator takes lengths in metres and depth in centimetres. A 5 m by 4 m area covered 5 cm deep is exactly 1 cubic metre, which is 1.31 cubic yards. In pea gravel that’s 1.83 to 2.09 US tons, or 1.66 to 1.90 metric tonnes. The weight per cubic yard stays in US tons, because that’s how the published figures are quoted. To convert a supplier’s tonnes per cubic metre, multiply by 0.843.

Common mistakes

1. Treating a cubic yard as a ton. A yard of rock weighs more than a ton. Order 5 tons for a 5-yard job and you’ll come up well short.
2. Leaving depth in inches. 10 x 10 x 3 is not 300 cubic feet. Three inches is a quarter of a foot. The calculator takes inches so you don’t convert.
3. Using the radius as the diameter. The circle shape wants the full width. Half of it gives a quarter of the rock.
4. Forgetting what’s already there. Topping up an old bed needs only the missing depth.
5. Trusting one website’s density. Including ours. The range is a planning tool until a supplier confirms it.

What the rock calculator can’t tell you

• Your supplier’s actual weight. Only their scale knows.
• Lava rock, decomposed granite and other materials. We don’t ship ranges for rock types we couldn’t source. Use “Other” with the supplier’s figure.
• Compaction. Crushed base packs down when rolled. Add waste for it.
• Delivery limits. Trucks carry a set weight, so a large order may come in more than one load.

More project calculators

For mulch, soil or concrete, where weight isn’t the issue, the cubic yard calculator gives volume and bags. Building a wall? The concrete block calculator counts blocks, mortar and core fill. For an asphalt driveway, try the bitumen calculator. Pool owners can use the pool salt calculator, and the job estimate calculator turns your quantities into a quote.

Sources

• Stone Center of Ohio, landscape rock calculator page: weights per cubic yard for pea gravel, river rock and crushed stone; recommended depths; 10% waste.
• Inch Calculator, river rock calculator: river rock 1.1 to 1.4 and gravel 1.4 to 1.7 tons per cubic yard; 2 to 4 inch depths.
• Omni Calculator, river rock calculator: densities in kg/m³ for river rock, pea gravel and crushed stone.
• Southwest Boulder & Stone, coverage calculator: 1 cubic yard = 1.25 tons rule of thumb.
• Bedrock Landscaping Materials, yardage calculator: coverage per ton by depth and for large rock; 10% for compaction.
• All checked on October 2, 2026. One cubic yard is 27 cubic feet, or 0.7646 cubic metres.