Topsoil Calculator
How much topsoil an area needs at a given depth — the volume, the weight at a bulk density, the number of bags, and the cost with a wastage allowance — in metric or imperial units.
Volume is area times depth, and topsoil is bought by the cubic metre, the tonne or the bag.
How the topsoil calculator works
Volume is area times depth, and topsoil is bought by the cubic metre, the tonne or the bag. Loose topsoil weighs about 1.1 to 1.3 tonnes a cubic metre depending on moisture, and settles by a tenth or so once laid, which the wastage allowance covers. Bagged soil is expensive per litre but convenient for small beds; bulk delivery wins above a cubic metre.
Formula: volume = area × depth × (1 + wastage); tonnes = volume × bulk density; bags = ⌈volume / bag size⌉
Worked examples
| Inputs | Topsoil to order | Note |
|---|---|---|
| A 40 m² bed at 150 mm | 6.6 m³ (7.92 t) | about 6.6 m³ |
| A thin top-dressing | — | a bagged job |
| Heavy, wet soil | 6.6 m³ (9.9 t) | more tonnes for the same volume |
FAQFrequently asked questions
How deep should topsoil be?
About 100 to 150 mm for a new lawn or bed, 300 mm or more for vegetables and shrubs, and 20 to 30 mm for a top-dressing over an existing lawn.
How much does topsoil weigh?
Roughly 1.1 to 1.3 tonnes per cubic metre loose, more when wet or clay-heavy. Suppliers quote by the tonne or the cubic metre; the density links the two.
Why add wastage?
Fresh topsoil settles by 10 to 15% as it beds in, and some is lost to uneven ground. Order a little over rather than come up short.
Bags or bulk?
Bags for under half a cubic metre or awkward access; bulk delivery for anything more — it is usually a third the price per litre, though it needs somewhere to tip.
Do I include the existing soil?
No — this is the new material only. If the ground is being raised, measure from the existing level; if replacing poor soil, from the excavated level.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Brick Development Association — brick sizes and quantities — 215 × 102.5 × 65 mm, 60 bricks per m²
- UK Government — Approved Documents (Building Regulations) — Building Regulations guidance
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.