Landscape Rock Calculator

Every landscape rock order starts with a volume. Multiply the length of the bed by its width to get square feet, then multiply by the depth in feet. Because you measure depth in inches, divide by 12 first. A bed of 200 square feet at 3 inches deep holds 50 cubic feet. Divide cubic feet by 27 to get cubic yards, the unit most quarries and landscape yards sell by. That bed is 1.85 cubic yards.

The second step is weight. Rock is often sold by the ton, and a ton of dense rock covers less ground than a ton of light rock. The calculator multiplies the volume by the density of the rock type you choose, then divides pounds by 2,000 for short tons. In metric the same steps use metres, centimetres, tonnes and kilograms per cubic metre.

The third step is the order. The extra percentage covers rock that sinks into soft ground, spreads beyond the edging and fills low spots. Ten percent is the default. Bags are counted from the order volume and rounded up, so you never come up one bag short.

This page is written for landscape beds, borders, tree rings and decorative areas. If you are laying a driveway or a base, the numbers are the same but the depth and stone grade are different, and the related calculators at the end of this guide are a better fit. If you also work in the metric system, the same area times depth sum gives cubic metres and tonnes, which you can read from the metric results.

Landscape rock comes in four common families. Crushed rock has sharp, angular faces that lock together. River rock is rounded and smooth. Decorative or pea gravel is small, rounded stone, and lava rock is light, porous and often red or black. The calculator has a density for each so the tons are realistic.

For crushed rock we use the Washington State Department of Transportation figures for loose, truck-measure crushed surfacing, 2,850 to 2,950 pounds per cubic yard. The middle, 2,900 pounds, is 107.4 pounds per cubic foot. For river rock we use one published sample of river stone with a loose bulk density of 1,474 kilograms per cubic metre, 92.0 pounds per cubic foot. That is a single sample, so treat it as a sensible average, not a guarantee. Dry gravel is 105 pounds per cubic foot in a common engineering reference table.

Lava rock has no standard figure we could verify, and real products vary a lot with how porous the stone is. The 50 pounds per cubic foot in the calculator is a placeholder. Use your supplier's number in the custom density box.

Wet rock weighs more than dry rock because water fills the gaps. If your pile has been rained on, or the supplier weighs a wet load, expect a few percent more. This is one more reason the delivery ticket, not the estimate, is the final word.

Depth does more than anything else to decide the quantity, so it is worth getting right. Extension advice for small rock mulch is a layer of 3 to 4 inches. That is deep enough to block most light from reaching weed seeds, and thick enough that the stone does not show the soil or fabric below as it shifts.

A thinner layer of 2 inches is common as a decorative cover over fabric. It saves money, but it shows wear sooner, and the stones sink into soft soil. If your rock is large, make the layer at least as deep as two to three stones, or it will look patchy. For paths and play areas, 3 to 4 inches inside a firm edging is a good range.

Deeper is not better. Past 4 inches the extra stone adds weight and cost without helping the weeds, and it makes plants harder to reach. The exception is a dry creek bed, where the channel is often deeper than the banks so that stones stay in place in a storm.

If this is a playground, the rules change. The CPSC Handbook for Public Playground Safety sets a minimum of 9 inches for pea gravel, and the surface depends on the fall height of the equipment. A decorative 3 inch bed is not a safety surface.

Coverage is the question most people type into a search box: how much ground does a ton cover? The answer depends on depth and on the density of the rock, so there is no single figure. At 3 inches, one cubic yard covers 108 square feet of any rock, because that is just volume over depth. One ton of crushed rock covers about 74 square feet at 3 inches, while a ton of the lighter river rock covers about 87.

To estimate quickly, divide 324 by the depth in inches to get square feet per cubic yard. At 2 inches that is 162, at 4 inches it is 81. Then divide by the tons per cubic yard of your rock, about 1.45 for crushed rock, to get square feet per ton.

The calculator shows both coverage figures for the depth and rock type you choose. Use the coverage per ton when your supplier prices by the ton, and the coverage per cubic yard when they sell by volume. If a quote and the calculator disagree by more than 10 percent, ask the supplier what weight per cubic yard they assume, since that is where the difference usually hides.

Two extras decide how well a rock bed ages: the fabric under it and the edging around it. Utah State University Extension describes woven landscape fabric as very effective for weed suppression, able to let water and air through, and resistant to tearing when rock is the top cover. You spread the fabric over the soil, cut holes for plants, then add the rock.

Fabric is not a cure-all. Other extension advice points out that a deep, correctly applied mulch can control weeds without it, and that fabric can get in the way of soil health in planted beds. For a path or a pure rock area, fabric is a good idea. For a bed with perennials, think about it first.

If you use it, buy more than the bed area, because the sheets overlap and the edges turn up at borders. We add 10 percent. A 20 × 10 ft bed needs 220 square feet. Edging is the perimeter: 2 × (length + width) for a rectangle, or pi x diameter for a circle. The default bed needs 60 feet. Edging also keeps the rock out of the lawn, which saves a lot of mower damage.

Bags make sense for small jobs. A bag of 0.5 cubic feet holds 1/54 of a cubic yard, so a job that needs one cubic yard is 54 bags before extra, or 60 with 10 percent. At that point a bulk delivery is usually cheaper and quicker, even with a delivery fee. Bag labels differ, so check the volume on the one you buy, and pick the matching size in the calculator.

For bulk orders, ask whether the yard sells by the ton or by the cubic yard. A yard sold by weight gives you the tons figure to quote. A yard sold by volume wants cubic yards. The calculator shows both, and the price box can take either.

Leave room to move the pile. A dump truck leaves rock in one heap, and you will be moving it by barrow, so tarp the drive and ask for the pile to be set as close to the bed as possible. Order a little more than you think, since a second small delivery often costs nearly as much as the first. Any rock left over is useful for filling low spots later.

Prices in the calculator are placeholders you replace with a real quote. The estimate covers material only. It does not include delivery, tax, fabric or edging.

The crushed rock calculator mode here works in square metres too. Switch to metres, centimetres and kilograms, and the same area times depth sum gives cubic metres. A 6 × 2 m border at 7.5 cm deep is 0.90 cubic metres, and with extra you order 0.99. At about 1,721 kilograms per cubic metre, that is 1.70 tonnes.

The result is an estimate. It assumes a flat, level bed with an even layer, a loose dry density and an exact depth. Slopes, soft ground, boulders and curved shapes all change the real figure. Crusher run and other graded mixes pack tighter than clean stone, so ask the quarry for its weight per cubic yard when you can. Your delivery ticket and the supplier's own figures take priority over this estimate.

When the numbers matter, for example a drainage bed or a retaining job, follow local requirements and the supplier's specification rather than a general estimate, and ask a qualified contractor to check.

A rock bed is rarely the whole job. If you are laying stone for a driveway, path base or fill, the Gravel Calculator uses the same area, depth and density idea with gravel in mind. The River Rock Calculator is tuned for river stone beds and dry creek beds, and the Stone Calculator covers crushed stone grades such as base and drainage rock.

If the new bed borders a lawn, the Grass Seed Calculator helps with the patch you will repair after the digging. Measure twice, order a little extra, and compare the supplier's weight per cubic yard with the figure in the calculator before you pay.