Landscape Rock Calculator
Decorative gravel, marble chips, slate, lava rock and DG – each with its own density, so the tonnage is right.
- Yards, tons, bags & cost
- US & metric units
- Free, no sign-up
Add a price for a cost estimate
How this was calculated
On this page
Decorative landscape rock replaces mulch for good – no annual top-ups, no fading, no blowing away. But because the stones range from feather-light lava rock to dense granite chips, a cubic yard can weigh anything from 0.7 to 1.4 tons. This calculator uses the right density for each type so your landscape rock tonnage comes out right, and shows cubic yards and bags alongside.
How to use the landscape rock calculator
- Measure each bed
Most planting beds are not rectangles. Break the bed into a few rectangles, circles or triangles and add them with “Add another area” – or pace out the square footage and use “I know the area”.
- Choose the depth
Over landscape fabric, 2″ is enough for small chips and 3″ for 1–3″ rock. If you are not using fabric, add an inch. Around tree trunks keep rock a few inches away from the bark.
- Pick the rock type
Decorative chips, marble, slate, lava rock, river rock and decomposed granite are all here with their own densities. Lava rock is about half the weight of the others – a big saving if you are carrying bags.
- Subtract plants? Usually not.
Plants, shrubs and stepping stones take up less area than you think and the rock settles around them. Only subtract large features like a patio or a pond.
Landscape rock formula
Cubic yards = Area (sq ft) × Depth (in) ÷ 324 (because 1 yd³ covers 324 sq ft at 1″)Tons = cubic yards × tons-per-yard for the rock (1.35 decorative gravel · 0.68 lava rock · 1.42 DG)
Example: 250 sq ft of beds, 3″ of 3/4″ decorative gravel
- Volume = 250 × 3 ÷ 324 = 2.31 yd³
- Weight = 2.31 × 1.35 = 3.1 tons
- Same area in lava rock: 2.31 × 0.68 = 1.6 tons – half the weight, same coverage
Landscape rock types compared
| Rock | Look | Weight (tons / yd³) | Good for | Watch out for |
|---|---|---|---|---|
| Decorative gravel / chips (3/4″) | Angular, grey-tan-brown mixes | 1.35 | Beds, borders, paths, modern designs | Sharp edges – not for bare feet |
| River rock 1–3″ | Smooth, rounded, multicoloured | 1.35 | Natural beds, dry creeks, around foundations | Rolls – needs edging |
| Pea gravel | Small, smooth, tan | 1.30 | Paths, patios, play areas | Migrates; weeds if no fabric |
| Marble chips | Bright white, angular | 1.28 | Formal beds, contrast against dark foliage | Raises soil pH slightly; shows dirt |
| Slate chips | Flat, blue-grey or plum | 1.22 | Contemporary gardens, around containers | Flat pieces can slide on slopes |
| Lava rock | Red or black, porous | 0.68 | Xeriscapes, fire pits, lightweight roof gardens | Very light – blows and floats; fades |
| Decomposed granite (DG) | Fine, sandy, packs hard | 1.42 | Paths, patios, between pavers | Tracks indoors; needs stabiliser on slopes |
| Boulders / rip rap | Large accent stone | 1.49 (placed) | Accents, slopes, retaining | Priced per piece or per ton – measure volume separately |
Coverage: square feet per ton of landscape rock
| Material | Density | Tons per yd³ | sq ft per ton at 2" | sq ft per ton at 3" | sq ft per ton at 4" |
|---|---|---|---|---|---|
| Decorative gravel / chips (3/4") | 100 lb/ft³ | 1.35 | 120 | 80 | 60 |
| River rock 1–3" | 100 lb/ft³ | 1.35 | 120 | 80 | 60 |
| Pea gravel | 96 lb/ft³ | 1.30 | 125 | 83 | 63 |
| Marble chips | 95 lb/ft³ | 1.28 | 126 | 84 | 63 |
| Slate chips | 90 lb/ft³ | 1.22 | 133 | 89 | 67 |
| Lava rock | 50 lb/ft³ | 0.68 | 240 | 160 | 120 |
| Decomposed granite (DG) | 105 lb/ft³ | 1.42 | 114 | 76 | 57 |
| Rip rap / boulders (placed) | 110 lb/ft³ | 1.49 | 109 | 73 | 55 |
Coverage = 2,000 lb ÷ (density × depth in feet). Figures are for loose material; add 5–10% for waste and up to 20% for compacted base layers.
Rock or mulch? The ten-year maths
Rock costs more up front – often three to five times the price of bark mulch for the same bed – but mulch needs topping up every year or two as it decomposes and washes away. Over ten years a bed mulched annually usually costs more than the same bed covered once in rock. Rock also does not feed weeds, harbour termites or wash into the lawn. The trade-off is heat: dark rock warms the soil, so in hot climates use it around drought-tolerant plants and keep organic mulch for thirsty beds.
Installing landscape rock: a short checklist
- Strip grass and weeds, then grade the bed so it slopes away from the house.
- Install edging first – it sets your finished height.
- Lay non-woven landscape fabric, overlapping seams by 6″ and pinning every 3 ft.
- Spread rock to the planned depth with a rake. Keep it 2–3″ below siding and away from trunks.
- Hose it down to wash off quarry dust and reveal the true colour.
Frequently asked questions
How much landscape rock do I need for 100 square feet?
At 2 inches deep you need 0.62 cubic yards; at 3 inches 0.93 cubic yards. In tons that is 0.8 / 1.25 tons of decorative gravel, or only 0.4 / 0.6 tons of lava rock.
How many square feet does a ton of landscape rock cover?
Depends on the rock. At 2″ deep, a ton of 3/4″ decorative gravel covers about 120 sq ft, marble chips about 126 sq ft, slate about 133 sq ft, and lava rock about 240 sq ft. At 3″ deep, take two-thirds of those figures.
How deep should landscape rock be?
2 inches for small chips over fabric, 3 inches for 1–3″ rock, 3–4 inches if there is no fabric underneath. Deeper than 4″ wastes money and makes planting harder.
Do I need landscape fabric under rock?
Strongly recommended. Fabric stops the rock sinking into soil (so you need less of it), blocks most weeds, and makes removal possible later. Use a non-woven, water-permeable fabric – not plastic sheeting, which kills the soil underneath and floods beds.
How much does landscape rock cost?
Bulk decorative rock typically runs $40–$120 per ton, with lava rock, marble and slate at the upper end and plain crushed gravel at the lower end. Bagged rock (0.5 cu ft) is $4–$10 a bag. For most beds over 150 sq ft, a bulk delivery is cheaper even with the delivery fee.
