Topsoil Calculator
Calculate how much topsoil you need for a new lawn or garden bed, including an allowance for settling – in cubic metres, tonnes and 25 L bags.
Formulas shown on this page · Last reviewed October 2026
How the topsoil calculator works
volume (m³) = area (m²) × depth (mm) ÷ 1,000
order (m³) = volume × (1 + settling allowance)
tonnes = order (m³) × density (kg/m³) ÷ 1,000
Loose topsoil weighs roughly 1,200–1,400 kg/m³ (about 1,300 kg/m³ is used by default). Freshly spread soil settles by around 15–20% as it is watered and compacted, so the calculator adds 15% to the volume you enter.
How deep should topsoil be?
| Project | Depth |
|---|---|
| Levelling or patching an existing lawn | 25–50 mm |
| New lawn from seed or turf | 100 mm |
| Flower and shrub beds | 150–300 mm |
| Vegetable beds and raised beds | 200–300 mm |
Buying topsoil in Australia
Common products include screened garden soil, turf underlay and garden mix. Landscape supplies yards sell soil by the cubic metre, delivered by truck or loaded into a trailer; bagged soil in 25–30 L bags suits small beds and pots. Many Australian soils are sandy or heavy clay, so a quality garden mix over the top improves water retention in dry summers. Lay turf soon after spreading so the soil does not dry out.
At the default prices, a 25 L bag is $7.00, or about $280 per cubic metre, while bulk soil is roughly $65 per m³ before delivery. Bulk is usually cheaper once you need more than about half a cubic metre. These are typical prices – check your local supplier.
Frequently asked questions
How much topsoil do I need for a 10 × 5 m lawn at 100 mm?
The base volume is 5 m³. With a 15% settling allowance you should order 5.75 m³, which weighs about 7.5 tonnes at 1,300 kg/m³.
How many 25 L bags is that?
5.75 m³ is 5,750 litres, so you need 230 bags of 25 L (rounded up) – about $1,610 at the default price.
Is topsoil cheaper by the cubic metre?
Usually yes for larger jobs. At the defaults, 5.75 m³ costs about $374 in bulk versus $1,610 in bags, before delivery.
Why add an allowance for settling?
Loose soil compacts as it is raked, watered and walked on. Without an allowance your finished level can end up 15–20% lower than planned.