What it works out
This works out how much gravel, topsoil, sub-base or sharp sand you need to cover an area to a depth: the volume, the weight, and how many bags or bulk bags that is.
Use it for a gravel path or drive surface, a new lawn or bed, or the sub-base under a patio or shed base.
How it works
The volume is the area times the depth. The waste allowance goes on top, then the volume is turned into a weight using the usual density for the material: topsoil is lighter than gravel, and a compacted sub-base heavier. If your supplier gives a different figure, type it in under More options.
The weight is then split into the bags or bulk bags you choose, in your region's sizes. For a loose load, it gives the tonnes and the cubic metres, because suppliers sell by either.
A worked example
An area 5 m by 3 m, covered with gravel 5 cm deep, in bulk bags of 850 kg.
- Area 1: 5 m × 3 m = 15 m²
- Volume: 15 m² × 5 cm = 0.75 m³
- 0.75 m³ + 10% for waste = 0.825 m³ × 1,700 kg/m³ (typical for gravel) = 1.4 t
- 1,402.5 kg → 2 bulk bags of 850 kg
The result
- Gravel1.4 tBuy 2 bulk bags of 850 kg (1,700 kg)
- Volume, with waste0.825 m³
These are the calculator's own figures for these measurements, with 10% for waste. Change any of them above and it works it out again.
Common mistakes
- Measuring the depth before compacting. A sub-base loses depth when it's compacted. Enter the depth you want once it's down.
- Assuming a bulk bag is a tonne. Bag sizes vary by supplier and country. Check the weight, or the volume, on their page.
- Laying gravel too deep. Deep gravel is hard to walk on and shifts underfoot. A layer just thick enough to hide what's underneath is usually enough.
- Skipping the membrane. A weed membrane under gravel keeps it from mixing with the soil and cuts down on weeding.
Questions people ask
How much gravel do I need?
Multiply the area by the depth to get the volume, and by the gravel's density to get the weight. The calculator does both and splits it into bags.
How many bulk bags is that?
The weight divided by the bag's weight, rounded up. The calculator uses the usual bulk bag size in your region; change it if your supplier's differs.
How much topsoil for a new lawn?
Choose topsoil, enter the area and the depth you want to add, and the calculator gives the volume and weight. Topsoil settles, so allow a little extra.
Can I use this for a drive?
For the gravel on top, yes. The sub-base under a drive needs designing for the vehicles and the ground, so ask a groundworker or an engineer for its depth.
Why does the same volume weigh different amounts?
Materials have different densities. A cubic metre of compacted sub-base weighs much more than a cubic metre of topsoil. The working shows the figure used.