Topsoil Calculator
Calculate how much topsoil, compost or growing media you may need — in m³, tonnes, bulk bags and small bags. Includes 2026 UK pricing and BS 3882 quality guidance.
Screened topsoil: ~1.60 t/m³. Ideal for lawns, borders and raised beds.
Area = π × (diameter ÷ 2)²
New lawns: 100–150mm. Raised beds: 200–300mm. Top dressing: 10–20mm.
Working in inches? 1 inch ≈ 25mm • 2 inch ≈ 50mm • 4 inch ≈ 100mm • 6 inch ≈ 150mm • 12 inch ≈ 300mm
Topsoil compresses as it settles. 15% is standard for screened topsoil. Compost may need 20–25%.
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Topsoil & Compost Comparison
The four common UK growing media options compared side by side. Screened topsoil is the default for most lawn and border projects.
Buying Guide
How to Calculate Topsoil
The Formula
Volume (m³) = Length (m) × Width (m) × Depth (m). For example, a 5m × 4m area at 100mm depth needs 5 × 4 × 0.1 = 2m³ of topsoil.
Always add a settling factor — typically 15% for screened topsoil, up to 25% for compost — to ensure your beds and lawns reach their intended final depth after the soil compresses.
Bulk Bags vs Small Bags vs Loose Loads
Small 25–40L bags are ideal for tiny areas and tight access (through a narrow gate or house). They are the most expensive way to buy topsoil per litre — typically 3–5× the cost of bulk bags. Check for multi-buy deals: B&Q and Wickes regularly run 3-for offers that reduce the per-bag price by 15–30%.
Bulk bags (jumbo bags, 1T bags) hold approximately 0.7m³ and weigh 800–1,000kg. They are the most common choice for garden projects and offer much better value than small bags.
For large projects over 5m³, a loose tipped delivery — where a tipper lorry deposits a heap of topsoil directly on your driveway — is usually the cheapest option, costing around £150–£250 for 5–10 tonnes.
Topsoil vs Compost — Which Do You Need?
Topsoil is the structural base: it contains minerals, has good drainage properties and provides physical support for roots. Compost is nutrient-dense organic matter that improves soil fertility but lacks structure.
For a new lawn or border, a 70/30 mix of topsoil to compost is ideal. For top dressing an established lawn, use finely screened topsoil alone. For raised beds, a 50/50 mix gives good drainage and fertility — or use a dedicated raised bed compost mix.
Why Topsoil Settles — The Science
Freshly delivered topsoil has a high air void ratio — particles are loosely packed with air pockets between them. This is why it looks voluminous straight from the bag. When watered, walked upon or subjected to rainfall, these air pockets collapse as fine particles fill the gaps. This process is called consolidation, and it is irreversible without mechanical intervention.
Screened topsoil typically consolidates by 10–15%. Compost, being almost entirely organic matter, can consolidate by 20–25% as the organic material begins to decompose. This is why you should always order more than your nominal volume calculation suggests — the settling factor is not a safety margin, it is a physical certainty.
Rain Gardens & SuDS — 2026 Guidance
From 2024, Schedule 3 of the Flood and Water Management Act requires Sustainable Drainage Systems (SuDS) for most new developments in England. Rain gardens are a low-cost SuDS solution suitable for domestic properties — a planted depression filled with permeable growing media that captures and slowly releases rainwater rather than sending it straight to the drain.
A rain garden requires 400–600mm of permeable growing media — typically a mix of sharp sand, topsoil and organic matter — to allow water infiltration whilst supporting plant growth. Use the Rain Garden preset in the calculator above and select a low-peat or peat-free mix to ensure permeability is maintained over time.
BS 3882:2015 — UK Topsoil Quality Standard
In the UK, quality topsoil is governed by British Standard BS 3882:2015, which defines three grades for different applications and requires suppliers to declare pH, nutrient levels and freedom from contaminants.
Multipurpose topsoil — the most common grade, suitable for general landscaping, turfing and domestic gardens. pH typically 5.5–7.5.
Specific purpose topsoil — tailored for acidic or alkaline-loving plants, or low-fertility requirements such as wildflower meadows.
Always ask your supplier for a Declaration of Compliance or Soil Analysis Report confirming the material is free from heavy metals or toxic substances, particularly for vegetable growing.
FAQ
Common Questions
Multiply the length and width of your area (in metres) to get m², then multiply by the depth in metres. A 5m × 4m area at 100mm depth = 2m³. Add 15% settling to get your order quantity — so order 2.3m³. Our calculator does this automatically.
A standard UK bulk bag holds approximately 0.7m³ of screened topsoil, weighing around 800kg–1 tonne. Divide your total volume (including the settling factor) by 0.7 to get the number of bags. For example, 2.3m³ ÷ 0.7 = 3.3, so order 4 bulk bags.
At 100mm depth, 1 tonne covers approximately 6–7m². At 50mm depth it covers 12–15m². At 10mm (top dressing), 1 tonne covers around 60–70m². These figures assume dry screened topsoil at 1.6 t/m³.
Screened topsoil has been passed through a mesh to remove large stones, roots and debris — resulting in a fine, consistent material ideal for lawns, borders and raised beds. Unscreened topsoil is raw excavated soil that may contain larger rocks and is better suited for filling deep voids or as a base layer under screened topsoil.
For a new lawn, a mix of 70% screened topsoil and 30% compost gives the best results — the topsoil provides structure and drainage, the compost adds nutrients for grass establishment. If you are top dressing an existing lawn, use finely screened topsoil on its own as compost can cause thatch build-up.
Topsoil is naturally aerated and fluffy when first delivered. As it is watered, walked on and exposed to rain over the first few weeks, it compresses. Screened topsoil typically settles by 10–15%, compost by 20–25%. Without accounting for settling, your beds will end up below your intended final level.