Gravel calculator

Gravel is bought in two different units, and mixing them up is the usual reason people end up with half a load too much or too little. Landscape bags and small delivered loads are sold by volume (cubic feet or cubic yards). Quarries and bigger deliveries are sold by weight (tons). The calculator gives you both, plus a bag count, so you can match whatever your supplier quotes.

Measure the area

Gravel goes where the ground is, and ground is rarely a clean rectangle. Measure length and width in feet at the widest and narrowest points. If the two readings differ by more than a foot or so, take three or four readings along the length and average them. Odd shapes are easier to split into rectangles and circles; our guide to measuring irregular areas walks through that.

Then decide the depth you want after the stone is compacted. That final figure matters because loose stone shrinks when it is rolled or tamped.

The formula in plain words

Multiply length by width to get square feet. Multiply that by the depth in inches. Divide by 324. The answer is cubic yards.

The 324 is just 27 cubic feet in a yard times 12 inches in a foot, folded into one number so you can keep depth in inches.

To get weight, multiply cubic yards by the tons-per-yard figure for your stone. Most crushed stone and gravel lands between 1.35 and 1.5 tons per cubic yard (about 2,700 to 3,000 lb). Pea gravel is reported anywhere from 1.25 to 1.6 tons, depending on which supplier you ask.

Worked example: a patio base

A 12 ft by 14 ft patio needs 4 inches of compacted base stone.

1. Area: 12 x 14 = 168 sq ft.
2. Volume: 168 x 4 / 324 = 2.07 cubic yards.
3. Compaction allowance: suppliers quote 10 to 20 percent for base stone that gets compacted, so add 15 percent. 2.07 x 1.15 = 2.39 cubic yards.
4. Weight at 1.4 tons per yard: 2.39 x 1.4 = 3.34 tons. At the low and high ends of the range (1.25 and 1.5), that is 2.98 to 3.58 tons.

Order about 3.5 tons, or 2.5 cubic yards if your supplier sells by volume. If you are buying 0.5 cubic foot bags instead, the same job takes 2.39 x 27 / 0.5, or about 129 bags.

In metric: 3.66 m by 4.27 m (15.6 square metres), a 10 cm layer, roughly 1.8 cubic metres or 3.0 metric tonnes.

Choosing a depth

Use the finished, compacted depth for the job:

• Decorative gravel over landscape fabric: 2 to 3 inches.
• Garden paths: 3 to 4 inches.
• Base under pavers: about 4 inches compacted.
• Gravel driveway surface: 4 to 6 inches. One government soil-and-water district guide asks for a minimum of 6 inches.

The longer breakdown, including what changes on soft soil, is in how deep should gravel be.

Types of gravel and how they differ

Pea gravel is small, smooth and rounded, about the size of a pea. It looks tidy, drains well and feels pleasant underfoot, but the stones roll against each other and never lock together. It works for paths, play areas and decorative beds, and badly on slopes or as a driveway base.

Crushed stone, such as #57, is angular, washed, and roughly 1/2 to 1 inch. The sharp faces interlock, so it stays put and drains freely. It is the usual choice for drainage trenches, the top layer of a driveway and loose-fill bases.

Crusher run (also sold as crush and run, 3/4 minus, ABC or dense-grade aggregate) is crushed rock mixed with its own fines. It packs into a firm, almost solid layer, which is why it goes under pavers and slabs. It drains poorly compared with clean stone. Names vary by region, so describe what you want to the supplier.

River rock is rounded stone, mostly 1 inch and up, bought for looks and drainage swales. Larger cobbles leave more air gaps, so a yard of them weighs a little less than a yard of small gravel.

Bags or bulk

A 0.5 cubic foot bag holds under 2 percent of a cubic yard, so a yard is 54 of them. Bags make sense for a path you can walk in a day or stone that has to go through a gate. For a driveway or a large base, bulk is the normal route. See bags vs bulk for how to find your own break-even point.

Common mistakes

• Ordering loose depth. If you measure 4 inches loose and then compact it, you end up with about 3.5. Order for the finished depth.
• Mixing tons and yards. A supplier quoting "5 yards" and one quoting "5 tons" are quoting different amounts of stone, about 7 tons versus 5 yards.
• Forgetting the haul weight. A cubic yard of crushed stone weighs 2,700 to 3,000 lb, more than many half-ton pickups should carry in a single load.
• Using round stone where you need grip. Pea gravel under a patio or on a driveway slope migrates.
• Skipping the weed barrier or base. Without a base, gravel sinks into soft ground over a couple of seasons.

Densities here come from supplier pages, not a standard, so treat the ton figure as a plan-ahead number and ask for the weight on the delivery ticket.

Values this calculator uses

Weights are loose, dry, typical figures in US tons (2,000 lb). Your supplier's numbers win if they differ.

Sources

• rosevillerocksupply.com: how much rock gravel mulch do i need
• blog.harborsoils.com: cubic yard calculator landscape materials
• earthstonerock.com: cubic yards vs tons
• skynursery.com: bulk calculator
• stonecenters.com: calculator
• sakrete.com: all purpose gravel
• culpeperswcd.org: Dirt and Gravel Road BMP Guide Final January 28 2019
• uvm.edu: SW Friendly Driveways web v2