How Much Gravel Do You Need for a Driveway or Path?

Gravel is sold by weight but measured by volume, and the conversion between them is where most orders go wrong. Order short and you are paying a second delivery charge for half a load.

Three measurements decide the whole order

Length, width and depth. Length and width are straightforward for a rectangle. For an L-shaped drive, split it into two rectangles and add them. For a curved bed, measure the longest and widest points and accept that you will over-order slightly, which is the right side to err on.

The US example above: 20 ft by 10 ft is 200 square feet. At 4 inches, or 0.333 feet, that is 66.7 cubic feet. Divide by 27 to get cubic yards, which gives 2.47. Gravel runs roughly 1.4 to 1.7 US tons per cubic yard depending on stone size and moisture, so at 1.5 that is about 3.7 tons.

The metric example: a 6 m by 3 m path is 18 square metres. At 50 mm, or 0.05 m, that is 0.9 cubic metres. At a bulk density near 1.6 tonnes per cubic metre, that is about 1.44 tonnes. Bulk bags are commonly around 850 kg, so two bags deliver 1,700 kg and leave about 260 kg spare.

Depth is where people get it wrong

A decorative top dressing over an existing solid base needs 40 to 50 mm, or about 2 inches. Any deeper and it feels like walking on sand. A gravel driveway that carries cars is a different job: 100 to 150 mm, or 4 to 6 inches, of compacted sub-base first, then 40 to 50 mm of decorative stone on top. Those are two separate calculations with two different materials, and running one calculation for the total depth will get you the wrong quantity of the wrong thing.

Turning volume into what the supplier sells

Suppliers quote in tonnes, US tons, cubic yards or bulk bags, and rarely in the unit you measured in. The conversions worth memorising: 1 cubic yard is 27 cubic feet; 1 cubic metre is about 1.31 cubic yards; a bulk bag is usually 800 to 900 kg, so roughly 0.5 cubic metres of gravel.

Density varies more than people expect. Wet gravel is heavier than dry. Small angular chippings pack tighter than rounded pea gravel of the same nominal size. If a supplier publishes a density for the specific product, use theirs rather than a generic figure.

Using the gravel calculator

Enter length and width in whatever units you measured, set the depth, and pick the material density if the tool offers it. The output is a volume plus a weight, and you order against the weight.

Read the result, then add a margin

Add 5 to 10% for settlement, spillage and the low spots you did not notice. On the 3.7 ton driveway that is another 0.2 to 0.4 tons, which is cheap insurance next to a second delivery fee. If you are also pouring an edging strip or a base slab, the concrete volume calculation works the same way with a different density. And if measuring the area is the awkward part, how to calculate square footage covers the odd shapes.

Common questions

How many bulk bags make a tonne? Usually a little more than one, since most bags hold 800 to 900 kg. Check the weight on the supplier's product page rather than assuming a bag is a tonne, because that assumption leaves you about 15% short.

Do I need a membrane underneath? For anything permanent, yes. A woven geotextile stops the stone working down into the soil and stops weeds working up. Without one, a 50 mm layer becomes a patchy 30 mm layer within a couple of seasons and you buy the difference again.

What stone size stops gravel scattering everywhere? Angular chippings around 10 to 20 mm lock together and stay put. Rounded pea gravel rolls, migrates to the edges, and gets carried away in tyre treads. Angular is the better choice anywhere vehicles turn.

Can I lay gravel straight onto grass? You can, and it will look fine for one summer. The grass dies, the surface goes soft, and the stone sinks. Strip the turf, level, compact, then lay the membrane.