Landscape Rock Calculator

How to calculate how much landscape rock you need

Landscape rock is sold by the cubic yard, by the ton or in small bags, and all three come from the same three measurements: length and width in feet and depth in inches.

Cubic yards = length (ft) × width (ft) × depth (in) ÷ 324
Tons = cubic yards × tons per yd³ (about 1.3 for decorative rock)

The 324 combines the 12 inches in a foot with the 27 cubic feet in a cubic yard, so you never convert depth by hand. The calculator above runs the same formula and also returns cubic feet, cubic metres, tonnes and the number of 0.5 ft³ bags.

1. Measure the bed. Split L-shapes and curved beds into rectangles, circles or triangles and add the areas.
2. Choose the depth. Small rock goes on thinner than large rock; the depth section below gives extension-service guidance.
3. Pick the preset. Landscape rock (1.3 tons per yd³) for decorative stone, river rock (1.35) for rounded stone, crushed stone (1.35) for angular #57-type stone. These are typical planning values, not figures from a published standard; if your supplier states a weight per yard, use theirs.
4. Add 10% for edges, low spots and the rock that works into the soil. The calculator’s waste field is set to 10% and you can change it.

Landscape rock for common bed sizes

Most beds fall into a handful of sizes. The table below gives the volume, weight and bag count at the two most common depths, 2 in and 3 in, using the calculator’s landscape rock preset of 1.3 tons per cubic yard. Every figure comes from the site’s calculation library.

To scale the table to another depth, multiply the 2 in row by half the new depth. A 10 × 20 ft bed at 4 in, for example, needs 2.47 yd³, about 3.21 tons, and at 6 in 3.7 yd³, about 4.81 tons.

How deep should landscape rock be?

The right depth depends mostly on rock size. Utah State University Extension advises 1 to 2 in of fine, dense material less than ½ in across, and 3 to 6 in of coarse, fluffy material between ½ in and 3 in across. USU gives these depths for mulch in general, rock included, so treat them as a starting range and check how your chosen rock covers the soil before ordering the full amount.

That guidance turns into very different orders. For a 200 ft² bed:

Going from 2 in to 4 in doubles the order, so settle the depth before you call the yard. If you are matching an existing bed, push a ruler through the rock in three or four places and average the readings; old beds are often thinner than they look because rock sinks into the soil.

How much does a ton of landscape rock cover?

One ton of decorative rock at 1.3 tons per cubic yard covers about 125 ft² at 2 in, 83 ft² at 3 in and 62 ft² at 4 in. Coverage per cubic yard does not depend on the rock at all, only on depth, so it is the more reliable column when you do not know the stone’s weight.

Working backwards from a load: 2 tons of landscape rock is about 1.54 yd³, enough for 249 ft² at 2 in or 166 ft² at 3 in. Five tons is about 3.85 yd³, which covers 623 ft² at 2 in or 415 ft² at 3 in. If you already have a tonnage and want yards, the tons to cubic yards converter does the division for any material.

Lava rock and other lightweight rock

Lava rock sold for landscaping is usually scoria or cinder. The U.S. Geological Survey describes scoria and cinder as irregular fragments of frothy lava. Because lava rock is porous, its weight per cubic yard can differ a lot from other landscape stone, so ask your supplier for the weight per yard of the product you are buying. That has two consequences for ordering.

• The volume is the same. A 10 × 10 ft bed at 2 in needs 0.62 yd³ of lava rock, exactly as it needs 0.62 yd³ of any other rock.
• The tonnage is not. The 1.3 tons per yard preset can overstate the weight of lava rock. Order lava rock by the cubic yard or by the bag, or ask the supplier for its weight per yard and multiply the cubic yards by that figure.

Lava rock pieces are usually coarse, so the 3 in end of the depth range applies. Washington State University Extension notes that crushed rock and lava rock mulch cannot blow away and resists compaction, but that debris eventually accumulates in it, which is worth knowing before you choose a light-colored rock that shows dirt.

Round beds, tree rings and odd shapes

A circle’s area is 3.1416 × radius², where the radius is half the diameter. For a ring around a tree, work out the outer circle and subtract the inner circle you leave bare. The table gives full circles at 2 in and 3 in deep; for a tree ring, subtract the trunk circle (a 1 ft trunk is 0.79 ft²). You can also choose Circle in the calculator and enter the diameter.

These bag counts have no waste added; add a bag or two per ring. For a kidney-shaped or curving bed, lay a garden hose around the edge, then measure the longest length and the average width at three points. Length × average width is close enough for ordering rock because the 10% allowance covers the rest.

Landscape rock in metric

Outside the US, decorative stone is sold by the tonne, the cubic metre or in bulk bags. At 1.3 US tons per cubic yard, the landscape rock preset works out to about 1.54 tonnes per m³. That is a planning value; use your merchant’s figure when they give one.

A 3 × 8 m front border at 50 mm is 3 × 8 × 0.05 = 1.2 m³, about 1.85 tonnes, or 2.04 tonnes with 10% extra. Bulk bag weights and volumes differ by merchant, so read the stated weight before you count bags.

Rock or mulch: what changes in the order

Rock and organic mulch are measured the same way, but they behave differently once they are down. Clemson Cooperative Extension points out that rock retains heat and raises ground temperature, that weed seeds can find their way into the gaps between stones, and that rock does nothing for plant growth or soil health, while its main advantage is low maintenance once it is in place. University of Arizona Extension adds that rock and gravel mulches collect heat and can increase cooling costs for the home and irrigation costs for the landscape in summer.

For ordering, the practical differences are these:

• Rock is bought once. It does not break down, so you size the bed for the full depth now rather than planning a yearly top-up the way you would with the mulch calculator.
• Rock is heavy. A cubic yard of mulch is easy to move by wheelbarrow in a few trips; a cubic yard of rock weighs far more (the calculator plans on about 1.3 tons per yard; use your supplier’s weight). Plan where the truck can tip it.
• Rock is hard to remove. If you might replant the bed with annuals later, mulch is the easier choice.

Bags or bulk landscape rock?

Bags make sense for small beds and top-ups; bulk makes sense once the bag count climbs. A cubic yard is 54 bags of 0.5 ft³, 36 bags of 0.75 ft³ or 27 bags of 1 ft³, so even a modest 10 × 20 ft bed at 3 in, at 110 bags with the allowance, means a lot of loading, unloading and opening. The same bed is about 2 yd³ from a landscape yard.

Bags still have a place. They suit a rock you only need a little of, a bed with no truck access, a rooftop or courtyard, or a decorative accent where you want to see the exact color before committing. They also keep small amounts tidy for later repairs. When you compare, convert both to the same unit: divide 27 by the bag size in cubic feet to get bags per yard, then compare that many bags with one yard of bulk rock delivered.

For bulk orders, ask whether the yard measures rock by the loader bucket or by weight on a scale. If they sell by the ton, multiply your cubic yards by their weight per yard; if they sell by the yard, the calculator’s cubic-yard figure is the order. Either way, round up to their smallest unit rather than down, because a second small delivery usually costs more than the extra rock.

Common mistakes when ordering landscape rock

• Using the wrong weight for lightweight rock. Lava rock and some pumice-type products weigh far less than the 1.3 tons per yard preset. Order those by the yard or bag.
• Ordering coarse rock at a fine-rock depth. Utah State University Extension advises 3 to 6 in of coarse mulch between ½ in and 3 in across, compared with 1 to 2 in for fine material under ½ in. Ordering coarse rock at a fine-rock depth falls short of that guidance.
• Forgetting the beds you subtract. Large shrubs, boulders and paths take space. Subtract them, then add the 10% allowance.
• Measuring depth on the surface. An existing bed may look full but be only an inch thick where rock has sunk into soil. Probe it before topping up.
• Mixing up yards and tons on the quote. A cubic yard is a volume and a ton is a weight, so “3 yards” and “3 tons” are different orders. The calculator assumes about 1.3 tons per yard as a planning value; ask your supplier for their rock’s weight per yard. Ask which unit the price uses; the calculator’s price field is set to tons.
• Leaving no room for the delivery. A bulk load needs a firm, accessible spot near the bed. Check with the supplier where their truck can tip.

Landscape rock vs river rock, gravel and pea gravel calculators: which one to use

All of these pages use the same volume formula; they differ in the weight per yard, the depths discussed and the jobs covered.

• Landscape rock calculator (this page): decorative rock, lava rock and crushed stone used as mulch in beds, borders and around trees, with a 2 in default depth.
• River rock calculator: rounded, water-worn stone for beds, dry creek beds and downspout splash areas.
• Gravel calculator: gravel for bases, paths and patios, including crusher run and compacted layers.
• Pea gravel calculator: small round stone for walking surfaces and play areas.
• Decomposed granite calculator: fine granite grit for paths and patios, natural or stabilized, by yard or ton.
• Mulch calculator: bark and wood mulch measured in cubic yards and 2 ft³ bags.
• Cubic yard calculator: any shape and any material when you just need the volume.

Before you order

Call the supplier with three numbers: the cubic yards from the calculator, the depth and the rock you want. Ask whether they sell that rock by the yard or the ton and, if by the ton, what a yard weighs. If their weight differs from 1.3 tons, multiply your cubic yards by their figure for an accurate tonnage. Ask about the smallest load they deliver and where the truck can tip, then add the 10% allowance and round up to the unit they sell.

If the bed is next to the house, check where downspouts discharge, and ask your siding manufacturer or local building department how much clearance to leave between the finished rock surface and the siding and weep openings. Rock is permanent, so it is worth spending ten minutes with a tape measure before the truck arrives.