How much topsoil do I need?
Last reviewed 1 July 2026
Short answer
Multiply the area by the depth, then add 20% for settlement. A 40 m² lawn at 100 mm needs 4 m³ of finished soil, so order about 4.8 m³ — roughly 6.5 UK bulk bags, or 4,800 litres. Screened topsoil weighs about 1,300 kg/m³, so that order is around 6.2 tonnes.
Work it out for your project with the topsoil calculator →
The calculation
- Work out the area. Beds are rarely rectangles, so split them into rectangles, circles and triangles.
- Multiply by the finished depth you want, in metres. 150 mm is 0.15 m.
- Add the settlement allowance — 20% is a sensible default.
- Convert to litres (× 1,000), bulk bags (÷ 0.73 m³) or cubic yards (× 1.308).
ordered volume = area × finished depth × (1 + settlement %)
Why settlement matters more here than anywhere else
Freshly screened topsoil arrives aerated. It has been dug, screened, loaded and tipped, and it is full of voids. Once it is watered, walked on and worked, it consolidates — typically by 10–25% depending on how organic it is and how it is placed.
A raised bed filled level on the day of delivery will commonly sit 40–80 mm lower after a few weeks. That is not soil disappearing, it is soil settling.
Ignoring settlement is the single most common reason a topsoil order comes up short, and topping up later means a second delivery charge for a fraction of a bulk bag.
Note: Organic blends settle most
Volumes for common jobs
| Job | Area | Depth | Finished volume | Order | Bulk bags |
|---|---|---|---|---|---|
| Lawn top dressing | 50 m² | 10 mm | 0.50 m³ | 0.60 m³ | 1 |
| New lawn | 40 m² | 100 mm | 4.00 m³ | 4.80 m³ | 7 |
| Flower border | 12 m² | 250 mm | 3.00 m³ | 3.60 m³ | 5 |
| Raised bed 2.4 × 1.2 m | 2.88 m² | 400 mm | 1.15 m³ | 1.44 m³ | 2 |
| Levelling a lawn | 80 m² | 50 mm | 4.00 m³ | 4.80 m³ | 7 |
Bulk bags taken as 0.73 m³. Check the stated volume with your supplier — topsoil bags vary from 0.6 to 0.8 m³.
Weight and access
Screened topsoil is about 1,300 kg/m³ when moist, and considerably heavier after rain. A 4.8 m³ order is around 6.2 tonnes, which is a tipper load and needs somewhere to tip.
Have boards or a tarpaulin down before the lorry arrives. Soil tipped straight onto a block-paved driveway stains it, and soil tipped onto a lawn kills the grass beneath within a day or two.
Plan the barrow route. Six tonnes is roughly 60 barrow loads, and if the route crosses a lawn you will want scaffold boards down.
Do not confuse topsoil with compost
- Topsoil is mineral soil, around 1,300 kg/m³, sold to BS 3882 grades in the UK. It is what you build a lawn or a bed from.
- Compost is organic, often 400–700 kg/m³, and is a soil improver rather than a bulk fill. Filling a deep raised bed entirely with compost gives you a bed that sinks dramatically and dries out.
- Blended topsoil sits between the two and is what most garden centres sell as premium topsoil.
- The density difference is why a bulk bag of compost feels light and a bulk bag of topsoil does not.
Related questions
- How many bulk bags of topsoil in a cubic metre?
- About 1.4 if the bag holds 0.73 m³. Topsoil bulk bags are sold by volume rather than weight because soil density varies so much with moisture, so always check the stated volume.
- How much does a cubic metre of topsoil weigh?
- Around 1,300 kg for screened, moist topsoil, with a realistic range of 1,100 to 1,500 kg. Saturated soil can exceed that.
Safety notice: Material planning only