Driveways, paths and drainage — volume, tonnes and bulk bags of gravel or aggregate you need to order.
Multiply length × width × depth to get volume in cubic metres, then convert to weight. Loose gravel and aggregate weighs about 1.6 tonnes per cubic metre, and a standard bulk bag holds around 800kg. Always add a waste allowance — gravel compacts and spreads unevenly.
Volume is 20 m² × 0.05 m = 1 m³. Gravel runs about 1.6 tonnes per cubic metre, so that is 1.6 tonnes — a full bulk bag is around 850 kg, so order two bags (or 1.7 tonnes loose) and keep the surplus for topping up after the first winter.
For driveways, 14–20 mm angular gravel knits together and stays put under tyres. For garden paths, 10 mm is kinder underfoot. Avoid pea gravel on driveways and slopes — it rolls out of place and migrates into drains. Gravel-look resin or bound surfaces cost far more but need no raking.
Gravel has no structural strength of its own, so a driveway still needs 75–100 mm of compacted Type 1 sub-base underneath, and rigid edging (kerb, timber or steel) on every open side to stop the stone spreading. Lay on a weed membrane to stop the stone sinking and to slow weeds. Keep the finished level about 15–20 mm below any DPC and give the surface a slight fall away from the house.
Bulk bags are the easiest option where a lorry cannot reverse close to the job: one bag covers roughly 17 m² at 50 mm. Loose tipper loads of 8–16 tonnes work out far cheaper per tonne on a large driveway, but you need clear access and somewhere to tip. For borders and small beds, 25 kg bags avoid a mountain of leftover stone.
Spreading it too thin (under 40 mm) so it wears through to the membrane; skipping the membrane and watching weeds push up; laying it flat with no fall so water sits; and putting rounded stone on a slope, where it will end up at the bottom of the drive within a season.
50–100mm is typical for a domestic gravel driveway over a compacted sub-base. A parking area for heavier vehicles wants the deeper end of that range.
A standard 800kg bulk bag covers roughly 10–12 m² at 50mm depth. Use the calculator to get an exact figure for your dimensions.
Yes — lay a permeable membrane over the sub-base before spreading gravel. It stops weeds and keeps the stone from sinking into the soil.