How to measure for topsoil
Measure the area you want to cover. For a rectangular lawn or bed, take the length (A) and the width (B). New lawns are rarely true rectangles, so check the width at both ends and in the middle and use the average. A round bed is a circle: measure straight across the middle. A corner bed is a triangle, and a lawn that wraps round a patio is an L-shape: measure it as a full rectangle, then the length and width of the missing corner. Use Add another area for each separate piece.
The depth is the thickness of new soil you want once it has been firmed, not the depth of any hole. If you are raising the level, lay a straight plank across the area and measure from the existing ground up to the finished level at a few points, then use the average. If you are replacing poor soil, the depth is how much you dig out.
Topsoil is sold by volume, in bags and bulk bags, but merchants who deliver loose soil often quote tonnes, so the calculator gives both. If you measure in feet and inches, switch the units at the top of the topsoil calculator. UK suppliers still sell in litres and cubic metres, and that is how the answer comes out.
Recommended topsoil depths
How deep the new soil needs to be depends on what will grow in it. Grass roots stay near the surface, shrubs and perennials go deeper, and root vegetables need the most. These are the depths Rolawn and the RHS give for new topsoil. The buttons in the table set the calculator to each one.
| Use | Topsoil depth | Apply |
|---|---|---|
| New lawnUnder turf or seed: at least 100 mm. | 100–150 mm of topsoil | |
| Border or new bedMost shrubs and perennials. | 150–200 mm of topsoil | |
| Vegetable bedRoot crops need the most depth. | 300–400 mm of topsoil |
Each button starts at one figure from the range, shown in the depth box. Change it to suit your ground: where the soil underneath is poor or compacted, the deeper end gives roots more room.
How much topsoil per m²?
Each square metre of topsoil spread 100 mm deep is 0.1 m³, which is 100 litres. That makes the sums easy: every 10 mm of depth over one square metre takes 10 litres. Double the depth and you double the litres, which is why deep borders and vegetable beds run into bulk bags so quickly.
To turn litres into weight, multiply the cubic metres by the density, typically 1.3–1.7 t/m³. Wet soil weighs more than dry, so suppliers’ figures vary. If yours gives one, open Density under the depth and type it in: the tonnes change, but the number of bags does not, because bags are sold by volume.
How much topsoil do I need for a new lawn?
Topsoil for turf or seed needs enough depth for the roots to find water in a dry summer. Rolawn and the RHS suggest 100–150 mm of good topsoil under a new lawn. Pick New lawn and the calculator starts at the lower figure; raise it if you can, especially over poor ground.
Rake the soil level, firm it by treading across it, then rake again before you lay turf or sow. The extra allowance covers the soil that disappears as you firm it. For the lawn itself, the turf calculator works out the rolls and the grass seed calculator the seed.
Topsoil to level lawn hollows
There is no levelling preset, because we found no UK source that gives a quantity for it: it depends entirely on how deep your dips are. Measure each hollow as its own area (a circle or a rectangle is usually close enough), then lay a straight plank across it and measure the gap underneath at a few points to find the average depth.
If the hollows are roughly the same depth, enter each one with Add another area and type the average depth. If one is much deeper than the rest, work it out on its own. Fill deep hollows a little at a time, firming as you go. For gentle unevenness across a whole lawn, gardeners spread a sandy top-dressing instead, which is a different product from the topsoil you buy for beds and new lawns.
Bags, bulk bags or a loose load?
For anything bigger than a small bed, bulk bags are the practical choice. A small bag covers well under one square metre at lawn depth, so even a modest new lawn runs to dozens of bags carried through the house. Under Buy it in you can choose the bulk bag and small bag sizes your supplier sells.
Some suppliers advertise tonne bags without saying how many litres they hold, so ask before you compare them. Used with the tonnes figure, this works as a general soil calculator. UK merchants who deliver loose soil by weight can work from the tonnes; garden centres and online suppliers sell by volume, so go by the bags.
Worked example: topsoil for a new lawn
Here is the full calculation for a rectangular lawn using the New lawn preset and the suggested extra for settling. Every line comes from the same code that runs the calculator above, so the figures always match.
- Area 8 m × 5 m = 40.00 m²
- Volume of topsoil 40.00 m² × 0.1 m (100 mm) = 4.00 m³
- Weight of topsoil 4.00 m³ × 1.5 t/m³ = 6.000 t (6,000 kg)
- Plus extra 6,000 kg + 10% = 6,600 kg (6.60 t)
- In bulk bags 4,400 litres ÷ 750 litres = 5.87, rounded up = 6 bulk bags
On the list:
- 6bulk bags of topsoil (0.75 m³ each)6.60 t needed
Notice that the bags are worked out from the litres, not the weight: the tonnes are there for suppliers who quote by the tonne. For a lawn this size the calculator goes straight to bulk bags. Enter the same measurements above and the ways-to-buy table under the result shows how many small bags it would take instead, which is a lot to carry through a house.
UK topsoil bag sizes
Topsoil in the UK is sold by volume. Small bags from DIY stores and garden centres are easy to carry but add up quickly. Rolawn’s standard bulk bag holds 500 litres and its large one 750 litres. Bulk bags are delivered by lorry and usually left on the drive or at the kerb, so check there is room and a firm surface before you order. The biggest jumbo bags need a lorry with a crane to set them down.
| Product | Size | Good for |
|---|---|---|
| 25 litre bag | 25 litres | Small DIY-store bag of topsoil. |
| 30 litre bag | 30 litres | Small bag of topsoil. |
| 35 litre bag | 35 litres | Small bag of topsoil or compost. |
| Bulk bag, 0.5 m³ | 500 litres | The standard bulk bag from several topsoil suppliers. |
| Bulk bag, 0.75 m³ | 750 litres | A common large bulk bag of topsoil or compost. |
| Jumbo bag, 1.2 m³ | 1.20 m³ (1,200 litres) | The largest bag; needs a lorry with a crane to deliver. |
A bag’s volume is measured loose, as it is filled. Topsoil settles once it is spread, firmed and watered, which is why suppliers suggest ordering 10–25% extra. The calculator starts at the lower figure; raise it for deep beds, and use the raised bed soil calculator for raised beds.
Common mistakes when ordering topsoil
- Comparing suppliers by weight. A bag’s weight depends on how wet the soil is. Compare by litres or cubic metres instead.
- Forgetting it settles. Loose topsoil firms down after treading and rain. Without the extra allowance, a bed filled level with its edging ends up below it.
- Spreading too thin under turf. A thin skin of new soil over hard ground dries out quickly in summer. Keep to the lawn depth in the table above.
- Using ordinary topsoil to top-dress a lawn. Top-dressing is a separate, sandy product spread very thinly. Topsoil is for filling and building up.
- Mixing up millimetres and centimetres. A depth of 100 typed as centimetres instead of millimetres asks for ten times too much. If the calculator says a depth looks unusual, check the unit.
What else you'll need
- Turf for a new lawn. The turf calculator works out the rolls for the same area.
- Grass seed if you are sowing instead: the grass seed calculator gives the grams and the packs.
- Compost or soil improver to dig into a new border before planting: use the compost calculator.
- Soil for raised beds, a blend of topsoil and compost with more allowance for settling: try the raised bed soil calculator.
- A rake, a spade and a wheelbarrow, plus a sheet or tarpaulin to protect the drive where the bulk bags are emptied.
Last checked 28 October 2026