Gravel Calculator (UK)
Last updated: 12 August 2026
Work out how much gravel you need for a driveway, path or border. Enter the area and depth and get the answer in tonnes, bulk bags and 25kg bags, using real UK bulk densities.
How the calculation works
Volume = area × depth. We convert to tonnes using the bulk density of your chosen gravel, then to 850kg bulk bags. Rounded pea shingle sits at about 1.6 t/m³; slate is lighter at 1.4 and limestone heavier at 1.65, which is why the type matters when ordering by weight.
Coverage per bag is the reverse calculation, and it is the number most people actually want: one bulk bag over how many square metres at the depth you have chosen.
How deep should gravel be?
| Use | Depth | Bulk bag covers |
|---|---|---|
| Decorative border | 25–40mm | 13–21 m² |
| Garden path | 40mm | ~13 m² |
| Driveway (over sub-base) | 50mm | ~10 m² |
| Driveway, heavy use | 75mm | ~7 m² |
Going deeper than 50mm on a driveway makes gravel harder to walk on and causes rutting — depth is not a substitute for a proper MOT Type 1 sub-base underneath.
Gravel driveway build-up
A gravel driveway that lasts needs 100–150mm of compacted MOT Type 1 sub-base, a weed membrane, then 50mm of gravel. Without the sub-base the stone works into the soil and you are topping it up every year. A gravel grid or cellular paving system keeps the stone in place on any slope.
Frequently asked questions
How much gravel do I need per square metre?
At 50mm deep, allow about 0.08 tonnes (80kg) of gravel per square metre. So a 10 square metre path needs roughly 0.8 tonnes, which is one bulk bag.
How much does a bulk bag of gravel cover?
A typical 850kg bulk bag covers about 10 to 12 square metres at 50mm deep, or 13 to 15 square metres at 40mm. Lighter materials like slate chippings cover slightly more for the same weight.
How many tonnes of gravel is a cubic metre?
Around 1.6 tonnes per cubic metre for standard rounded gravel and pea shingle. Slate chippings are lighter at about 1.4 tonnes, and limestone or Cotswold chippings heavier at around 1.65 tonnes.
How deep should gravel be on a driveway?
50mm of gravel over a properly compacted MOT Type 1 sub-base. Deeper than that becomes difficult to drive and walk on and encourages rutting. The sub-base, not the gravel depth, is what makes a driveway durable.
What size gravel is best for a driveway?
14 to 20mm angular gravel locks together better than rounded pea shingle, which migrates under tyres. Pea shingle is better suited to paths, borders and decorative areas.
Related calculators
Aggregate Calculator
MOT Type 1, gravel, sand or topsoil — tonnes and bulk bags.
Block Paving Calculator
Paving blocks, sub-base and sand for a driveway or patio.
Concrete Calculator
Slab and footing volumes in m³, with bag counts or ballast & cement.
Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.