Gravel & Sand Calculator
Find how much gravel, sand, mulch or aggregate to order from the area and depth of your layer — in both cubic metres and tonnes, since suppliers sell by weight.
How to use this calculator
- Enter the area to cover and the depth of the layer in cm.
- Pick the material — density varies, and suppliers sell by weight.
- For a compacted sub-base, add ~10% since loose material settles.
Formula used
Depth in metres (5 cm = 0.05 m). Densities vary: gravel and sand ~1.6 t/m³, MOT type 1 ballast ~2.0, topsoil ~1.5, bark mulch only ~0.4. Wet or compacted material is heavier than these dry loose figures.
Example calculation
A 20 m² path at 5 cm gravel: 20 × 0.05 = 1.0 m³ × 1.6 = 1.6 tonnes.
That's about two bulk bags — and if it's a compacted sub-base, order ~10% more for settlement.
Ordering by weight, planning by volume
Aggregate suppliers sell by the tonne, but your project is defined by volume (area × depth) — so the density conversion is unavoidable, and it varies more than people expect. A cubic metre of dense ballast weighs five times a cubic metre of bark mulch, so ordering the right tonnage means knowing the material.
Depth choice drives cost as much as area: decorative gravel wants only ~5 cm, but a driveway sub-base needs 10 cm or more of compactable material to bear weight without rutting. And compacted layers settle — the loose delivered volume shrinks when rolled, so a sub-base needs roughly 10% extra ordered to finish at the target depth.
Why use this calculator?
- Convert your area and depth into the tonnage suppliers actually sell.
- Correct density for gravel, sand, ballast, topsoil or mulch.
- Bulk-bag estimate and a compaction reminder built in.
Frequently asked questions
How much gravel do I need?
Multiply area by depth for volume, then by ~1.6 for tonnes. A 20 m² area at 5 cm deep needs 1 m³ ≈ 1.6 tonnes of gravel. Enter your figures for the exact amount.
How deep should gravel be?
About 5 cm for decorative gravel over a membrane, 10 cm+ for paths and 15 cm+ (in compacted layers) for a driveway sub-base that carries vehicles. Deeper layers resist rutting and weed growth.
How many tonnes in a bulk bag?
Typically 0.5–0.8 tonnes, often quoted as "850 kg" or "one tonne" bags that are usually a bit under. Check the supplier's actual fill weight — it varies — and the calculator estimates the bag count at ~0.75 t each.