How Much Topsoil for a New Lawn? At Least 10cm, Seed or Turf

This page is about the soil a new lawn grows in. Scattering a little topsoil over overseeded patches so the birds don’t get the seed is a separate job, and the RHS covers it.¹ For that one, see mixing grass seed with topsoil.

How much topsoil for grass? 100 litres per m²

A new lawn needs at least 10cm (4in) of topsoil, whether you sow seed or lay turf. That’s the RHS minimum.² Rolawn, which sells turf and topsoil, goes a bit further: 100mm to 150mm “for turf or seed”.³

The sum is length times width times depth, everything in metres.³ So each square metre of lawn takes 0.1 cubic metres of topsoil at 10cm deep. That’s 100 litres, or 150 litres at 15cm. A bare 20m² plot takes 2 to 3 cubic metres. Knock off any good topsoil that’s already there.^M

That table is our own maths for bare ground.^M Get your exact figure and a bag count from the topsoil calculator.

Rolawn gives a reason to aim for the range, not just the floor: too thin a layer can hold the roots back, and too thick a layer may settle over time.³

Measure the topsoil that’s there. Buy only the gap.

Plenty of new lawns don’t need a full new layer. Rolawn says so itself, on the page selling its own lawn topsoil. It comes down to how deep and how good your soil is.⁴

Buy the full depth for ground that’s already half there and you’re paying for soil you don’t need. Grab a spade and a tape measure, and do the sum on the gap only.

1. Measure the lawn. Length times width in metres gives you square metres.
2. Dig a few test holes. Spread them across the plot and measure how deep the good topsoil goes, in centimetres.
3. Pick your target depth. That’s 10cm at least, the RHS minimum,² or Rolawn’s 10cm to 15cm.³
4. Work out the shortfall. Take the depth you’ve got off the target. If the holes already show the target depth or more, there’s no shortfall and you don’t need any.
5. Turn it into volume. Multiply the area by the shortfall in metres for cubic metres. Times 1,000 gives litres.
6. Count the bags. Check how many litres your supplier’s bag or bulk bag holds and divide.

Worked example. A 20m² plot, test holes showing 6cm of decent topsoil, target 10cm. The gap is 4cm, so 20 × 0.04 = 0.8 cubic metres, or 800 litres. Order as if the ground were bare and you’d buy 2,000 litres. That’s two and a half times as much soil, and you pay for all of it.^M If you can’t tell where the good soil stops, we’d play safe and work to the full depth.

Seed or turf: same depth, different prep

The depth doesn’t change. The RHS minimum covers laying any lawn,² and Rolawn’s 100mm to 150mm range applies to turf and seed alike.³ Its turf-laying guide sets 100mm as the floor for turf, with 150mm better.⁵ None of the sources we checked gives seed a lower figure.

What does change is the prep and the calendar.

• How deep you dig. For seed on hard, compacted ground, the RHS says dig or rotovate to about 20cm (8in).⁶ Turf wants deeper digging, 20 to 25cm (8 to 10in), so no compaction is left.⁷ Rolawn says cultivate turf ground to 100mm at least, 150mm ideally, while the soil’s fairly dry.⁸
• When. Sow in autumn (September to November) or mid-spring (March to April), says the RHS.⁶ Turf goes down best in mid-autumn, and any time until early spring if the soil isn’t too wet or frosty. Skip mid-spring to early autumn.⁷
• Delivery day. Turf wants laying within 24 hours of arriving if you can manage it, so have the ground ready first.⁷ Rolawn adds one job: water the soil 75mm deep two days before the turf turns up.⁸

Seed quantity lives on the grass seed calculator. Roll count lives on the turf calculator, which also shows the topsoil under the turf at Rolawn’s 100mm to 150mm.⁵

New-build gardens: the topsoil’s often gone

Roots often struggle behind a new house, and the RHS new-build guide explains why. On most developments the original topsoil is taken off during the build. Site traffic then packs down the subsoil left underneath. When soil is spread back for landscaping, rubble and spare aggregate can end up buried beneath it.⁹

So on a new build, don’t skip the test holes. The same RHS page says most new-build soil is short of nutrients. It wants at least a bucketful of organic matter per square metre, forked or rotovated into the dug ground.⁹ It gives two warnings as well. On clay in wet weather, a rotavator can leave a pan, a hard packed layer just under its blades. And a walk round the site in wet weather shows you where water sits.⁹

Prep the ground: topsoil first, surface last

Turf needs the same care with the ground as seed, the RHS says.⁷ Get the order right. New topsoil goes on first. Then let it settle, firm it and rake the top. Any pre-sowing or pre-turfing feed goes into that top layer with the rake.

1. Before the topsoil goes down

• Clear it. Rolawn says take out every stone and bit of debris bigger than 6mm, plus any perennial weeds.⁸
• Only add well-rotted organic matter. The RHS says dig in well-rotted manure or compost to hold moisture, mainly on sandy soil. Raw stuff shrinks as it breaks down and the lawn sinks in patches.⁷

2. Spread the topsoil

Spread the new topsoil over the cleared, dug ground until the good soil hits your target: 10cm at least (RHS) or 10cm to 15cm (Rolawn).²³ If there’s no shortfall, skip this step.

3. Settle it, firm it, rake it

• Let it settle. Leave dug ground a few days at the very least, and five to six weeks if you can, the RHS says.⁶⁷
• Firm it with your feet. Tread the whole area several times in different directions, with small shuffling steps.⁶ Don’t reach for a heavy roller, though. Rolawn warns it can compact the soil too much.⁵
• Rake it. Rake in several directions to a level, fine, crumbly seedbed, pulling out big stones and breaking up lumps.⁶
• Finish a touch high on dug-over ground. On an old flower bed the level can drop a little as it settles, the RHS says. Leave it slightly above the lawn you’re matching.⁷
• Feed for seed (optional). The RHS rate is 70g of general-purpose fertiliser per square metre.⁶
• Feed for turf on light, poor soil. A different RHS page says use the maker’s rate, or about 35g per square metre. Use the figure for your job rather than splitting the difference.⁷

Best topsoil for grass seed: pick the grade, check the load

The RHS sorts topsoil into three grades: premium, general-purpose and economy.² For a new lawn from seed, it points you to general-purpose. If you’re laying turf, go coarser, and keep the finer stuff for top-dressing. Economy is the cheap bulk option, often delivered unscreened, for filling space rather than for quality.²

The RHS says good topsoil should meet the British Standard, and it still names the 2007 edition.² The current one is BS 3882:2015, published on 30 April 2015; it covers topsoil that’s moved or traded, both multipurpose and specialist.¹⁰ Ask your supplier which edition their soil was tested to.

Before you accept a load:

• Ask to see a sample that’s typical of the whole load, and approve it before the delivery is booked.⁹
• Turn over a few spadefuls when it lands. Lots of stones, thick woody roots, weeds or bits of glass and brick are all warning signs.²
• Find out which site it was dug from, and whether the whole load came from there. The RHS notes a lot of it comes off building sites, where quality swings.²
• Knowing the source matters for another reason: imported soil can sometimes bring in Japanese knotweed or couch grass.²

Bulk bags aren’t a standard size. Rolawn’s lawn topsoil comes in bags of roughly 500 litres and 750 litres when packed.⁴ Our topsoil calculator assumes 850 litres a bulk bag. So check the litres stated for your supplier’s bag before you trust any bag count, ours included.

No tonnes on this page, on purpose. Rolawn itself says work topsoil out by volume, not weight, because moisture content varies.³

New-lawn topsoil isn’t lawn top-dressing

Topsoil and top-dressing do different jobs. Rolawn draws the line: topsoil is the layer you start a new lawn in, while top-dressing goes over an existing lawn as routine upkeep. It marks its lawn topsoil as unsuitable for top-dressing an established lawn.⁴

Top-dressing is a sandy mix. The RHS home-made version is three parts sandy loam, six parts sharp sand, one part peat-free multi-purpose compost.¹ For that job, use the lawn top-dressing calculator.

Frequently asked questions

Run the numbers for your lawn

Sources and checking notes

Every source below was read on 1 October 2026. Rolawn sells turf and topsoil, so its pages are quoted as Rolawn’s own advice, not as an independent authority.

1. Royal Horticultural Society, Repairing lawns. “Cover the seeds with a light sprinkling of top soil or home-made compost to hide them from birds”; top-dressing from “three parts sandy loam: six parts sharp sand: one part peat-free multi-purpose compost”. Accessed 1 October 2026.
2. Royal Horticultural Society, Topsoil: buying. “For laying lawns you will need at least 10cm (4in) layer of top soil”; “Topsoil is available in three grades: premium, general-purpose and economy”; “Good quality top soil should meet British Standards 3882:2007”. Accessed 1 October 2026.
3. Rolawn, Calculating topsoil requirements. “For turf or seed, aim for: 100mm to 150mm of topsoil”; “Too little topsoil can limit root growth, while too much can lead to settling over time”; “Topsoil is best calculated by volume, not weight, as moisture content can vary.” Accessed 1 October 2026.
4. Rolawn, Turf & Lawn Seeding Topsoil, the seller’s own product page. “Not every lawn will require additional topsoil”; “Standard bulk bag: approx. 0.5m³ / 500 litres when packed”; “Large bulk bag: approx. 0.75m³/750 litres when packed”; not suitable for “Topdressing an established lawn”. Accessed 1 October 2026.
5. Rolawn, How to lay lawn turf step-by-step. “Aim for a minimum topsoil depth of 100mm, with 150mm preferred”; “Avoid using heavy rollers, as these can compact soil too much.” Accessed 1 October 2026.
6. Royal Horticultural Society, Starting a lawn from seed. “If the soil is hard and compacted, dig or rotovate to a depth of about 20cm (8in)”; “Timing - Autumn (Sept-Nov) or mid-spring (March-April)”; fertiliser “at a rate of 70g (2oz) per sq m”. Accessed 1 October 2026.
7. Royal Horticultural Society, How to lay turf. “Dig or rotovate the soil to a depth of 20–25cm (8–10in)”; “Turf should be laid within 24 hours of delivery if possible”; “approximately 35g per sq m (1oz per sq yd)”. Accessed 1 October 2026.
8. Rolawn, Preparing to lay turf. “cultivated to at least 100mm deep, ideally 150mm”; “remove all stones and other debris (greater than 6mm) and any perennial weeds”; “water the soil to a depth of 75mm”. Accessed 1 October 2026.
9. Royal Horticultural Society, New-build gardens. “In new developments, existing top soil is usually removed”; “at least one bucketful per square metre”; “request a representative sample for your approval”. Accessed 1 October 2026.
10. BSI, BS 3882:2015 Specification for topsoil. Covers “natural and manufactured topsoils that are moved or traded”; published 30 April 2015, status current. Accessed 1 October 2026.

M — GardenCalc’s own arithmetic, not an external source. We multiply the lawn area (m²) by the depth or shortfall (converted to metres) to get cubic metres, and multiply that by 1,000 to get litres. The same method runs the topsoil calculator. The worked example and the table on this page were recomputed on 1 October 2026.

Left out on purpose: a settling allowance as a percentage, topsoil weights in tonnes, and any smaller depth for seed than for turf. None of the sources above gives a figure we could check for these, and the density figures we found disagree with each other, so they stay off this page until they can be sourced.