How to use the rock calculator
Pick your rock, then add each bed or path as a shape: a rectangle, a circle, a triangle, a ring around a tree, or an area you already know. Type how deep the rock should be. The page gives tons, cubic yards, pickup loads, bags if you type your bag size, the weed fabric to cover the beds and the edging around them. It is for decorative rock bought by coverage. Base and driveway stone is on the gravel calculator. Nothing you type leaves your device unless you make a share link.
How it is figured
tons = cubic yards × (1 + extra ÷ 100) × tons per cubic yard
sq ft one ton covers = 324 ÷ (tons per yard × depth in inches)
Rock is sold by weight, so the page finds the volume and multiplies by the weight of a loose cubic yard of your rock. The 324 is the square feet one cubic yard covers at 1 inch deep. For a bed 20 feet long and 10 feet wide with 3 inches of river rock, the area is 200 square feet and the volume is 200 × 0.25 = 50 cubic feet, or 1.85 cubic yards. With 3 percent extra for settling that is 1.91 yards. River rock is 1.4 tons a yard, so the order is 2.67 tons, rounded up to 2.75 tons, or 3 pickup loads at about a ton each. One ton covers about 75 square feet of that bed (77 before the extra). The page opens on this example.
How heavy is each rock
Typical weights for a loose cubic yard, with the range suppliers publish. Quarries and wet rock differ, so your supplier's figure wins.
| Rock | Tons per cubic yard used | Range seen | Starting depth |
|---|---|---|---|
| River rock | 1.4 | 1.3 to 1.75 | 3 in |
| Lava rock | 0.5 | 0.45 to 0.65 | 3 in |
| Decomposed granite | 1.4 | 1.35 to 1.4 | 2 in |
| Marble chips | 1.4 | one source | 2 in |
| Crushed granite | 1.4 | 1.35 to 1.5 | 3 in |
| Pea gravel | 1.35 | 1.3 to 1.4 | 3 in |
Lava rock is full of holes, so it weighs about a third as much as the rest. A truck fills up with it long before it reaches its weight limit.
Depth and coverage
Depth changes the answer most. For river rock, one ton covers about 231 square feet at 1 inch, 116 at 2, 77 at 3, 58 at 4 and 39 at 6. The Coverage chart tab lists every rock and depth, in tons or cubic yards, and prints. Rock thin enough to show the soil does not block weeds, so two to three inches is the usual range for beds. Decomposed granite is spread thin and packed, so it starts at 2 inches.
Settling and extra
Rock sinks a little and shifts as it is raked and walked on, so each rock starts with an extra percent that you can change. Fine, packable decomposed granite settles most, so it starts at 20 percent; the others are small. These are estimates, not measurements, so type your own if you know better. Landscape fabric underneath keeps the rock on top.
Flagstone
Flagstone is bought by weight too. The Flagstone tab takes your patio's length, width and thickness, the share that will be joints, and an extra percent for cuts and breaks. One guide gives 200 square feet a ton at 1 inch thick, 150 at 1.5 and 100 at 2. The page uses a flat 10 pounds per square foot per inch, which matches at 1 and 2 inches and runs a little heavier at 1.5, so it errs toward enough. It also counts stepping stones along a path.
Where the numbers come from
A cubic yard is exactly 27 cubic feet and a US ton exactly 2,000 pounds. A pound is exactly 0.45359237 kilogram, so a US ton is 0.90718474 tonnes. The rock weights come from supplier and landscape-stone pages we read, and the table shows where they disagree. A pickup load of about 1 ton is a rule of thumb; your truck's legal load is on its door sticker. No building code covers decorative rock. Press Metric to type meters and centimeters and see tonnes and cubic meters.
What people use it for
- River rock or lava rock beds around the house, with fabric underneath.
- Decomposed granite for a dry garden path or a patio.
- A dry creek bed, or where the downspout lands.
- Checking a quote: your supplier says tons, a bag says cubic feet, and this page ties the two together.
Common mistakes
- Using the gravel weight for lava rock. It weighs about a third as much, so you need more truck trips than the tons suggest.
- Guessing the depth. Measure with a ruler. Going from 2 to 3 inches takes half again as much rock.
- Skipping the fabric and the edging. Without fabric the rock sinks and weeds come through; without edging it spills onto the lawn. The page lists both.
- Ordering the exact number. Rock settles and spills. Keep the extra, and round up to what your supplier sells.
Questions
How many tons of river rock do I need?
Multiply the area in square feet by the depth in inches, divide by 324 for cubic yards, and multiply by 1.4. A 200 square foot bed 3 inches deep is about 2.7 tons with the starting extra.
How deep should landscape rock be?
Two to three inches is the usual range for beds. Thinner than that lets the soil show and weeds through. Decomposed granite is spread about 2 inches deep and packed.
What is the difference between this and the gravel calculator?
This page is for decorative rock sold by coverage. The gravel calculator is for base layers, driveways, drains and paver patios, and it adds layers and labor.
Does the calculator include a price?
No. It never shows a price of its own. If you type your price per ton, yard, tonne or cubic meter, it multiplies it by the order.
Can I use metric?
Yes. Press Metric to type meters and centimeters; the answer leads with tonnes and cubic meters. The page opens in your browser's region system and remembers your choice.
Can I share my result?
Yes: a Facebook link with a picture, a link to copy, and a TikTok video made on your device. The link keeps only the rock, shapes, sizes and depths, for 90 days, never your price.