How deep should topsoil be for lawns, beds and raised beds?

How deep should topsoil be for a new lawn?

At least 4 in (100 mm), and 6 in (150 mm) or more where you can manage it. That is the line New Mexico State and the University of Tennessee both draw (New Mexico State University Cooperative Extension (B. Leinauer) and University of Tennessee Extension (Samples, Sorochan)). Where soil is poor, add topsoil and organic matter to reach 4-6 in of total topsoil depth after firming. (New Mexico State University Cooperative Extension (B. Leinauer))

The phrase that matters is after firming. Loose soil spread from a barrow sits higher than it will once it has been rolled, walked on and rained on. Spread, firm, then measure again before seeding or turfing.

A common belief is that an inch or two of topsoil over hard subsoil is enough for new grass. The extension guides disagree: 4 in is the minimum, and the subsoil should be loosened first so roots and water can move down rather than sitting in a shallow layer on a hard pan (New Mexico State University Cooperative Extension (B. Leinauer), University of Tennessee Extension (Samples, Sorochan) and others).

UK lawns

The RHS frames it as preparation depth rather than a topsoil layer. Before turfing, the RHS says dig or rotovate to 20-25 cm (8-10 in) and let the ground settle, ideally five to six weeks. (Royal Horticultural Society (UK)) Figures of 150 mm for lawns and 300 mm for borders turn up in UK planning-application landscape specs, but we could not trace them to BS 3882 or to RHS text, so treat them as common practice rather than a standard.

How deep should soil be for borders and raised beds?

Deeper than a lawn. Shrubs and vegetables root further down than turf, and a raised bed has to hold all its own soil.

• Raised beds. USU says raised beds should be at least 6-12 in high; beds under 12 in should be open-bottomed over loosened soil. (Utah State University Extension) An open bottom lets roots carry on into the ground below, so a shallow bed borrows depth from the soil underneath.
• Improving an existing border. You rarely need to replace the soil. Miracle-Gro directs spreading 2-3 in of garden soil and mixing it into the top 6-8 in of native soil. (Scotts Miracle-Gro (label text as shown on Farm and Fleet listing)) That is a top-up of a few inches worked in, not a new layer sitting on top.

Bagged products are labelled by coverage. Miracle-Gro's label says three 1.5 cu ft bags cover 24 sq ft about 2 in deep, or four bags at 3 in. Those label counts line up closely with plain area × depth arithmetic, so you can work out bags yourself for any bed size.

Illustration sources

• Utah State University Extension — Raised Bed Gardening (Feb 2012)
• Scotts Miracle-Gro (label text as shown on Farm and Fleet listing) — Miracle-Gro All Purpose Garden Soil 1.5 cu ft

How do you work out how much topsoil you need?

Five steps, and the second one is the one people skip.

1. Measure the area. Length × width in feet or metres. Split curved beds into rectangles and triangles.
2. Probe the existing soil. Dig a few test holes with a spade and measure how much usable, crumbly soil is already there before you reach hard or stony subsoil. Only the shortfall needs buying.
3. Calculate the volume. Area (sq ft) × depth to add (in) ÷ 12 = cubic feet; ÷ 27 = cubic yards. In metric, area (m²) × depth (mm) ÷ 1,000 = cubic metres.
4. Convert to bags or a bulk load. Divide cubic feet by the volume printed on the bag and round up. For bulk, round up to the supplier's increment.
5. Spread, firm and re-measure. Spread in layers, firm each one, and check the depth again before final levelling. Top up low spots rather than ordering a percentage extra up front.

How much topsoil per 1,000 square feet?

Use this table to sanity-check a quote. Scale it to your area: a 500 sq ft lawn needs half these figures, a 2,500 sq ft lawn two and a half times. The University of Tennessee rounds the 4 in figure up to 12.5 yd3 per 1,000 sq ft (University of Tennessee Extension (Samples, Sorochan)).

Worked examples: a lawn and a raised bed

A 30 × 50 ft lawn, 4 in of new topsoil

A 1,500 sq ft (139 m²) lawn needs 18.5 cu yd (14.2 m³) of topsoil for a 4 in (100 mm) layer.

1. Area: 30 × 50 = 1,500 sq ft.
2. Volume: 1,500 × (4 ÷ 12) = 500 cu ft.
3. Cubic yards: 500 ÷ 27 = 18.5 cu yd. Cubic metres: 139.4 m² × 0.1016 m = 14.2 m³.
4. Check against the table: 1.5 × 12.35 = 18.5 cu yd.

If test holes showed 2 in of decent soil already there, adding 2 in to reach the minimum halves the order to 9.3 cu yd (7.1 m³). Going to the recommended 6 in total with 2 in already present means adding 4 in, which is the full 18.5 cu yd. Either way, loosen the ground underneath before spreading.

An 8 × 4 ft raised bed, 12 in deep

The bed holds 32 cu ft of soil, which is 1.19 cu yd or 0.91 m³ (906 L).

1. Volume: 8 × 4 × (12 ÷ 12) = 32 cu ft.
2. In 1.5 cu ft bags: 32 ÷ 1.5 = 21.3, so 22 bags.
3. In metric, a 2.44 × 1.22 m bed 0.305 m deep is 0.91 m³. Divide the litres by the volume printed on your bag.

At 22 bags, a single small bulk delivery is often easier to handle, but bulk-versus-bag prices vary too much by area to give a break-even point, and we found no source that publishes one. Two or three beds this size and bulk usually wins on handling alone.

Why does dug soil swell, and does topsoil settle?

Soil dug out of the ground takes up more room than it did in place, because digging breaks it into loose clods with air between them. That is why spoil from a hole never fits back in neatly, and why a level-looking delivery of topsoil sinks once firmed.

The WisDOT study behind most US earthwork conversions measured this for 14 natural soils. Loose dry unit weights of 14 natural soils tested for WisDOT ranged 66-106 lb/ft3 (about 0.89-1.43 short tons/yd3 dry, before moisture). (Wisconsin Highway Research Program / WisDOT (Cetin, Bulduk, Likos, Edil)) Clays swelled most when dug; clean sands barely changed.

How much does a yard of topsoil weigh?

We could not find a published figure for delivered, screened topsoil from a producer or an extension service, so we do not give one. The closest measured values are the WisDOT dry figures above, about 0.89–1.43 short tons per loose cubic yard before any water, and topsoil is rarely dry. Moist soil weighs more, and a load bought after rain covers the same area but weighs more on the ticket.

This matters for two things: whether a trailer or pickup can carry the load, and comparing a quote by the ton with one by the yard. Ask the yard for the weight of their product per yard or per bulk bag. For volume conversions on any area, the cubic yard calculator handles feet, inches and metric.

Likewise, no extension source gives a settling percentage for topsoil. Order for the depth you want after firming, and keep a little back for low spots rather than adding a fixed percentage.

Why is a few inches of topsoil worth protecting?

Because bare soil disappears faster than most people expect. USDA NRCS's 2022 National Resources Inventory found US cropland lost about 4.75 tons per acre per year to water and wind combined, and that 18% of cultivated cropland lost soil to water faster than its tolerable rate (USDA Natural Resources Conservation Service and Iowa State University CSSM). Those are farm figures, not garden ones, but they show how quickly an unprotected surface goes.

The same inventory counts about 120 million acres of developed land in the US by 2022, 40% of it built in the previous 40 years (USDA Natural Resources Conservation Service and Iowa State University CSSM). Much of today's lawn and garden ground sits on land that was graded within living memory, which is one reason test holes so often find thin soil over subsoil.

In practice: seed, turf or cover new topsoil soon after spreading. A layer of mulch on beds slows wash-off and drying; the guide on coverage per bag at each depth has the depths. And do not build on topsoil: a path or drive should go on firm subsoil, as the guide to gravel for a driveway explains.

What is in a bag of UK topsoil or compost?

Increasingly, less peat. Defra's latest datasheets show peat made up 24.1% of all UK growing media supplied in 2023, and only 16.6% of bagged retail products sold to gardeners (Department for Environment, Food & Rural Affairs (Defra)). In the older industry series, which used a different method, peat was 62.2% in 2011 (Horticultural Trades Association / Defra / AHDB (compiled by Paul Waller Consulting)).

Soil itself is a small part of what is sold in bags. Growing media products used 215,880 m³ of soil or loam in 2023, about 7% of the total (Department for Environment, Food & Rural Affairs (Defra)). Most bagged products are compost-type growing media, which are fine for raised beds and pots but are not a like-for-like substitute for topsoil under a lawn.

The government announced a ban on selling peat to amateur gardeners in England in August 2022, saying bagged retail growing media accounted for 70% of peat sold in the UK; the ban had still not been legislated by late 2026 (Defra (gov.uk) and UK Parliament (House of Commons)). As of 19 October 2026, the UK government said its 2024 and 2025 horticultural peat-use statistics had been delayed and were due by the end of 2026, so 2023 is the latest official year.

For a lawn or a border in the UK, buy screened topsoil by the bulk bag or the cubic metre and check what the supplier says it is made from. We could not confirm UK bag sizes or bulk-bag volumes from a manufacturer, so read the volume off the bag rather than assuming one.

When the depth figures do not apply

• Compacted or waterlogged subsoil. New topsoil on a hard pan holds water in a shallow layer. Loosen or drain the subsoil first; more topsoil does not fix drainage.
• Slopes. Loose soil on a bank washes down before roots hold it. Spread in thinner layers and cover quickly.
• Against the house. Raising ground level against a wall can bridge a damp-proof course or cover weep holes and siding. Keep the finished level below them.
• Over tree roots. Piling soil over an established tree's roots is a different question from lawn depth; ask an arborist.
• Unknown fill. Cheap "topsoil" can be subsoil or demolition fill. Look at a load before it is tipped.

For the other materials a garden project uses, see the yard and garden material tools, including the mulch calculator for what goes on top.

Bottom line

Aim for 4 in of topsoil as the floor and 6 in where you can, measured after firming, over subsoil you have loosened. Probe what is there before you order, buy only the shortfall, and cover it quickly. Raised beds need their full height in soil, and an existing border usually needs a few inches worked in rather than a new layer.

Topsoil depth questions