Topsoil calculator: how much topsoil do I need?
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Work out how many tonnes and bulk bags of topsoil a lawn, border or raised bed needs, with extra for the soil settling. Enter your measurements below; every figure we start from is shown and you can change it.
Worked example
| You enter | Value |
|---|---|
| What are you filling? | An area (lawn, border, path) |
| Area | rectangle 4 m × 2 m |
| Depth | 300 mm |
| Material | Topsoil |
| Density | 1.4 t/m³ |
| Settlement and waste allowance | 10% |
| Bulk bag size | 0.85 t |
| Small bag size | 25 kg |
Order: 5 bulk bags
| Result | Value |
|---|---|
| Bulk bags | 5 |
| Small bags | 148 |
| Weight | 3.7 t |
| Volume (with waste) | 2.64 m³ |
| Area | 8 m² |
Show the working
- Area: Area 1 8 m² = 8 m²
- Volume: 8 m² × 0.3 m = 2.4 m³
- With 10% waste: 2.4 × 1.1 = 2.64 m³
- Weight: 2.64 m³ × 1.4 t/m³ = 3.7 t
- Bulk bags: 3.7 t ÷ 0.85 t = 4.35, rounded up to 5
- Small bags: 3,696 kg ÷ 25 kg = 147.84, rounded up to 148
How it works
- Volume (m³) = area (m²) × depth (m) × (1 + waste)
- Weight (t) = volume (m³) × density (t/m³)
- Bulk bags = weight (t) ÷ bulk bag size (t), rounded up
- Small bags = weight (t) × 1,000 ÷ small bag size (kg), rounded up
Settlement: loose topsoil firms down as it's walked on, rolled and watered, so a bed filled to the brim ends up lower. The settlement allowance adds extra on top of the finished depth to cover this; change it if your supplier suggests a different figure.
BS 3882 sets out grades of topsoil. Ask your supplier which grade they sell and for its soil analysis.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Density: Topsoil | 1.4 t/m3 Sources range 1.4–1.5 t/m3 | Typical value Not yet checked against the source | rospower.co.uk tonnage calculator (exact page to confirm) (checked 19 October 2026) |
| Settlement and waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Allowance for settlement. |
| Bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
| Small bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common small bag. |
Regulations and standards
- BS 3882 (specification for topsoil): grades of topsoil; ask your supplier which grade they sell
Explained: BS 3882 (topsoil).
Our checks use the guidance for England unless a badge says otherwise. Wales, Scotland and Northern Ireland have their own rules: check the source for where you live.
FAQs
Guides
How much topsoil for a raised bed?
Measure a raised bed, allow for settling and choose bags or a bulk bag. What goes into a raised-bed mix.