United Kingdom · Materials & DIY
Topsoil Calculator
Change the bulk density used
Enter the area and the depth of soil you want. The calculator returns cubic metres, tonnes and bulk bags, and allows for the settlement that catches people out on raised beds.
How much topsoil do I need?
Multiply the area in square metres by the depth in metres, then by about 1.4 tonnes per cubic metre. A 10 m² bed filled to 300 mm needs 3 cubic metres, which is roughly 4.2 tonnes — around five bulk bags. Add 10 to 15% because loose soil settles noticeably once watered.
How to use this calculator
- Decide the settled depthLawn turf wants 100 to 150 mm of decent soil beneath it; vegetable beds want 300 mm or more; a levelling layer over existing ground may only need 50 mm.
- Measure the areaFor a raised bed, use the internal dimensions rather than the outside of the frame — the difference matters on a small bed with thick timber.
- Leave the 15% settlement allowance onLoose topsoil settles by a surprising amount once it is watered and walked on. Filling a raised bed exactly level with the top means it will sit 30 to 50 mm low within a fortnight.
- Read tonnes and bulk bagsTopsoil is usually sold by the bulk bag or the tipped tonne, so both are shown.
How the calculation works
Area by depth gives cubic metres. Cubic metres by bulk density gives tonnes. Simple enough, but topsoil has the widest density range of any material on this site, and that is where estimates diverge.
Screened loam sits around 1.3 to 1.4 tonnes per cubic metre. A clay-heavy soil after rain can approach 1.8. A peat-rich or heavily composted blend can drop below 1.2. That is a spread of more than fifty per cent, which on a five-tonne order is a difference of nearly two tonnes.
The practical implication is that ordering topsoil by weight without knowing the density is genuinely risky. Where a supplier sells by volume — cubic metres or a stated bag volume — you are on much firmer ground, because volume is what actually fills your bed.
tonnes = area × depth ÷ 1000 × 1.4Worked example: a raised vegetable bed
A raised bed with internal dimensions of 2.4 m by 1.2 m, filled to 400 mm, is 2.88 m² × 0.4 m — 1.15 cubic metres.
Add 15% for settlement and you want 1.32 cubic metres. At 1.4 tonnes per cubic metre that is 1.85 tonnes, or around two bulk bags.
The settlement allowance is doing real work here. Fill that bed to exactly 1.15 cubic metres and after the first proper watering the soil will sit roughly 50 mm below the frame — enough to look wrong and enough to reduce the rooting depth you built the bed for. It is far easier to add the extra at the start than to top up around established plants.
How deep, for what
| Use | Settled depth |
|---|---|
| Levelling over existing soil | 25 – 50 mm |
| New lawn from seed or turf | 100 – 150 mm |
| Ornamental borders | 300 – 400 mm |
| Raised vegetable beds | 300 – 500 mm |
| Deep-rooted crops and fruit | 500 mm or more |
For lawns specifically, the depth matters more than most people expect. Turf laid on 50 mm of topsoil over compacted subsoil will establish and then struggle in the first dry spell, because the roots have nowhere to go. The extra 50 mm at the start is far cheaper than a failed lawn.
Grades of topsoil, and why it matters
Not all topsoil is the same product. Screened topsoil has been passed through a mesh to remove stones and debris and is what most domestic jobs want. Unscreened or as-dug soil is cheaper and will contain stones, roots and the occasional surprise — fine for bulk levelling under turf, frustrating in a vegetable bed.
Blended or manufactured topsoil is made to a specification, usually mixing soil with green compost or sand, and is what you want for anything where drainage or nutrient content is critical. It costs more and is more consistent.
British Standard BS 3882 classifies topsoil quality, and reputable suppliers state which grade they are selling against it. Where a supplier will not say, assume as-dug — and be aware that soil sourced from a construction site can carry contamination and weed seed that will cost you far more in time than you saved on price.
Topsoil delivered wet weighs considerably more than the same volume dry, so a tonnage order after a wet week gives you less soil in the bed. Where you can, order by volume rather than weight.
Assumptions and limitations
- Assumes an even depth across the whole area
- Density defaults to 1.4 t/m³ — the real range across topsoil types is roughly 1.2 to 1.8
- The 15% settlement allowance is typical for loose soil that will be watered in; heavily composted blends settle more
- Does not account for existing ground level or the volume of any subsoil you dig out first
- Raised bed calculations should use internal dimensions, which the calculator cannot know
- Bulk bag counts assume 850 kg per bag, which varies by supplier and by soil moisture
Questions people ask about this in United Kingdom
How many tonnes of topsoil in a cubic metre?
Around 1.3 to 1.5 tonnes for screened topsoil, commonly taken as 1.4. Clay-heavy or wet soil can reach 1.8; a peat or compost-rich blend can be under 1.2. That range is why ordering topsoil by volume is safer than ordering by weight.
How much topsoil does a bulk bag cover?
A bulk bag holding roughly 850 kg is about 0.6 cubic metres of topsoil. At 100 mm deep that covers around 6 square metres; at 300 mm for a raised bed it covers about 2. Fill weights vary, so check with the supplier.
How deep should topsoil be for a new lawn?
At least 100 mm of good topsoil, and 150 mm is better. Turf laid on a thin skim over compacted ground establishes and then struggles in the first dry spell, because the roots have nowhere to go. The extra depth costs far less than relaying the lawn.
Does topsoil settle after it is laid?
Yes, noticeably. Loose soil compacts by 10 to 20 per cent once it is watered and walked on, which is why filling a raised bed exactly level leaves it sitting low within a fortnight. Order the settlement allowance and heap it slightly proud.
What is the difference between topsoil and compost?
Topsoil is mineral soil with some organic content and is the structural growing medium. Compost is decomposed organic matter used to improve it. Filling a bed entirely with compost gives you something that holds water badly, settles heavily and runs out of structure — use topsoil as the bulk and compost as the improver.
Should I buy screened or unscreened topsoil?
Screened for anything you are planting into or laying turf over — it has had stones, roots and debris removed. Unscreened or as-dug is cheaper and acceptable for bulk levelling that will be covered over. Ask which BS 3882 grade a supplier is selling against; a reputable one will tell you.
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Method, source and review date
- How it is worked out
- Volume by bulk density, with a settlement allowance
- Formula used
tonnes = area (m²) × depth (m) × 1.4 t/m³- Basis
- Typical supplier bulk densities, editable on the page
- Last reviewed
- Confidence
- Medium
Topsoil density varies widely with organic content and moisture — screened loam runs lighter than a heavy clay-based soil. Use your supplier's figure where they publish one.
Spotted a figure that has moved, or a formula you can show is wrong? Tell us — send a correction. Fixes to rates and formulas are treated as urgent.
Disclaimer
Quantities are an estimate for planning and ordering. Site conditions, wastage, cuts and delivery minimums all change what you actually need — always confirm with your supplier or the person laying the material before ordering.