Gravel Calculator

Gravel is the material where people most often order the wrong quantity, because suppliers sell it two different ways. Some sell by volume — cubic yards or cubic metres of loose material; others sell by weight — tonnes or US tons. This calculator gives you both, linked by the bulk density of the material you pick.

It covers rectangular, circular and triangular areas, takes a depth in inches or centimetres, and supports the common gravels and stone with their typical densities. There is also a bag option if you are buying in bags rather than having a load tipped.

Bulk density is not the density of rock

A solid cubic metre of granite weighs about 2.7 tonnes. A cubic metre of granite gravel weighs around 1.6 tonnes, and a cubic metre of pea gravel less still. The difference is the air in the gaps between the stones — anything from 30% to 45% of the total volume with loose, rounded material.

That is why bulk density, not the material's true density, is the number to use. It also means the weight of a given volume shifts with moisture and with how the material has settled in the pile: wet gravel can be 10–15% heavier than the same gravel dry, and material that has been sitting in a stockpile is more compacted than freshly tipped material.

Treat the weight this calculator delivers as an estimate for budgeting and comparison. For a large order, ask the supplier for their own conversion figure for that specific aggregate.

How deep should gravel be?

Depth is where most driveway and path projects go wrong, and it depends on what the gravel is doing:

• Decorative bed or mulch replacement: 2 inches (50 mm) is enough to cover the soil and suppress weeds.
• Garden path on a firm base: 2–3 inches (50–75 mm).
• Foot traffic over soft ground: 3–4 inches (75–100 mm).
• Driveway over a prepared sub-base: 4 inches (100 mm) of surface gravel on top of a compacted base course.
• Driveway where vehicles park: 4–6 inches, laid in two passes and compacted between them.

A driveway is very rarely just gravel. It is a compacted sub-base of larger crushed stone — typically 4–6 inches of 40 mm stone — with a 2–4 inch surface layer of smaller, finer gravel on top. Pouring decorative pea gravel directly onto soil and driving on it will simply push the stone down into the mud.

Worked example

A driveway 20 feet long and 10 feet wide, covered 3 inches deep. The area is 200 square feet, the depth is 0.25 feet, giving 50 cubic feet — 1.85 cubic yards, or 1.416 cubic metres. At a bulk density of 1.68 tonnes per cubic metre for gravel, that is 2.38 tonnes, or 2.62 US tons, or about 2,380 kilograms.

With a 10% wastage allowance — sensible for a driveway, where the sub-base is never perfectly flat — the order becomes about 1.56 cubic metres or 2.62 tonnes. Most suppliers round to the nearest half tonne, so you would ask for 2.5 or 3 tonnes.

Choosing between the types

Pea gravel is small, rounded and smooth. It drains well, feels good underfoot and looks tidy, and it is the right choice for decorative beds, paths and play areas. It is also the worst choice for a driveway, because rounded stones do not interlock and the surface will shift and rut under vehicle weight.

Crushed stone has angular faces that lock together when compacted, giving a stable, load-bearing surface. This is what driveways are built from. River rock sits between the two: larger than pea gravel, still rounded, and used for dry stream beds, borders and areas where appearance matters more than load.

For a driveway surface, a 20 mm crushed stone with fines — often called MOT Type 1, crusher run or road base — compacts to a firm, near-solid surface. For a top dressing, a clean 10–14 mm crushed stone gives a looser decorative finish that needs occasional raking.