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 the UK
Common products include general-purpose topsoil, screened topsoil and turf-grade topsoil. Garden centres sell 25 L bags, while merchants and landscapers supply bulk bags of about 0.75–1 m³ or loose loads by the tonne or cubic metre. With wet winters, avoid spreading topsoil when the ground is waterlogged and compact it lightly to prevent a soggy, uneven lawn.
At the default prices, a 25 L bag is £4.00, or about £160 per cubic metre, while bulk soil is roughly £42 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 £920 at the default price.
How many bulk bags of topsoil do I need?
A bulk bag holds roughly 0.85 m³ here, so 5.75 m³ needs 7 bags. Bulk bag sizes vary (about 0.75–1 m³), so check with the supplier.
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.