Lawn Top Dressing Calculator

By Gary Hodson · 15+ years UK gardening experience · Figures cross-referenced against RHS guidance and named UK supplier specifications · Last reviewed 4 July 2026

Top dressing is the habit that separates a decent lawn from a great one: a thin layer of sandy soil mix, spread over the grass and brushed in until it disappears. Rolawn's lawn aftercare guidance lists the payoffs plainly — top dressing assists in levelling the lawn, repairing worn and patchy areas, improving drainage and minimising thatch.² The RHS uses it as the follow-up to autumn aeration: a mix of loam, sand and well-rotted organic matter raked into the aeration holes to improve the soil structure in the root zone.¹

How Much Goes On

Far less than most people expect. The RHS rate is 2–3kg per square metre — about a shovelful at a time — worked in with the back of a rake or a broom.¹ UK suppliers of ready-mixed 70:30 dressing quote the same territory: 2kg/m² for a light dressing, 4kg/m² medium and 6kg/m² for a heavy dressing.⁴ Rolawn's volume-based rule is up to 3 litres per m² (about 3mm deep) in spring and autumn, and up to 1.5 litres per m² in summer.² The test of a good job is that afterwards the grass is clearly visible with no obvious clumps of dressing on the surface.²

Weight, Bags and Bulk Bags

Ready-mixed lawn dressing is sold by weight in 25kg bags⁴ and by volume in bulk bags — Rolawn's Lawn Topdressing bulk bag holds roughly 500 litres and covers up to 167m² at the 3-litres-per-m² rate.³ To convert between the two, this calculator uses a density of about 1.5kg per litre, implied by a named supplier's 70:30 spec (a 25kg bag covering 0.33m² at 50mm).⁵ Dressing is dense stuff: even a light pass over a 100m² lawn is 200kg of material, so check delivery access before ordering bulk.

Measuring an Irregular Lawn

Break the lawn into simple shapes. An L-shape is two rectangles; a lawn with a rounded end is a rectangle plus a half-circle. Measure each piece, then use the "+ Add this area" button in the calculator above to stack them into one running total. If you already know your total area, switch the calculator to "I know my area" and type it straight in. Remember to subtract anything inside the lawn that won't be dressed, such as paths, patios or beds.

Levelling Hollows

Top dressing levels a lawn gradually, not in one hit. Use the heavy 6kg/m² rate⁴ on the low areas and repeat over more than one season rather than burying the grass — Rolawn's maximums (3mm per application in spring or autumn) exist because a dressing the grass can't grow through smothers it.² For hollows deeper than a couple of centimetres, lift the turf, build the level up with topsoil and relay it instead.

The mix matters as much as the amount. All lawn dressings are variations on the same three ingredients — sand for drainage, soil or loam for body, and organic matter for the soil life — and the right blend depends on what your lawn sits on.

70:30 sand : topsoil — the ready-mixed UK standard. Most turf and topsoil suppliers sell lawn dressing as a 70% sports sand, 30% screened topsoil blend, in 25kg bags or bulk bags.⁴⁵ The high sand content keeps the dressing free-draining and easy to brush in, which is why it dominates the trade. If you're only buying one product, buy this.

The RHS DIY mix — 3 : 6 : 1. If you'd rather blend your own, the RHS recipe is three parts sandy loam, six parts sharp sand and one part well-rotted home-made compost or soil improver.¹ That's the sand-soil-compost family of dressings: the compost fraction adds organic matter, which earns its keep on tired, hungry lawns.

Sand-based dressings for drainage. Rolawn's own Lawn Topdressing is a sand-based, peat-free loamy sand designed to be brushed into the sward,³ and the RHS pairing of hollow-tine aeration plus top dressing is aimed squarely at compacted, waterlogging-prone lawns — the dressing rakes into the tine holes and improves the structure of the root zone.¹ If your lawn sits wet over winter, aerate first and favour the sandier end of the spectrum.

Whichever mix you use, buy it finely screened — coarse, lumpy material won't brush in, and Rolawn's finish test is that after working the dressing in there should be no obvious clumps on the surface, with the grass clearly visible.²

The golden rule from Rolawn's guidance: only top dress while the grass is actively growing, and never in drought conditions.² A dormant or drought-stressed lawn can't grow up through the dressing, so the dressing just sits there shading it out.

Early Autumn (September–October)

The classic window. The RHS carries out top dressing as part of its September–October lawn care routine, straight after scarifying and aerating — the dressing rakes into the aeration holes and improves the root-zone soil.¹ Rolawn puts autumn (with spring) in the "deeper application" category: up to 3 litres per m², about 3mm.² If you're overseeding the same season, this is when to do both.

Spring (once growth restarts)

The second full-rate window. Rolawn's spring guidance matches autumn — up to 3 litres per m² — because the grass is growing strongly enough to come up through the dressing.² Wait until the lawn is genuinely moving (you're mowing regularly) rather than dressing onto cold, wet ground.

Summer

Light maintenance only. Rolawn's summer rate is half the spring/autumn figure — up to 1.5 litres per m², about 1.5mm — and only when the grass is growing and watered, never during a dry spell.²

Winter

Leave it. Growth has stopped, so the lawn can't work the dressing through, and walking a laden barrow over wet winter turf compacts the very soil you're trying to improve. Wait for spring.

Conditions on the day

Apply when the grass surface is relatively dry so the dressing brushes in cleanly rather than smearing, water the lawn when you've finished, and don't mow immediately after applying the dressing.²

Top dressing is a half-day job on a normal garden lawn, and almost all of it is preparation. Here is the full sequence, drawn from RHS autumn lawn care and Rolawn's aftercare guidance.

Preparation (do this first)

• Mow the lawn. Cut the grass first so the dressing can reach the soil surface instead of sitting on long growth — and remember Rolawn's rule for afterwards: do not mow immediately after applying the dressing.²
• Scarify out the thatch. Rake out dead grass and moss — one of the jobs top dressing supports is minimising thatch,² but it can't do that through a mat of it.
• Aerate. Spike with a garden fork, or use a hollow-tine aerator on clay or waterlogged soil. The RHS treats top dressing as the step straight after aeration: the mix is raked into the holes to improve the root-zone soil structure.¹
• Pick a dry-ish day. Apply when the grass surface is relatively dry, while the lawn is actively growing — never in drought.²

Application

• Weigh out the right amount. Use the calculator above — RHS rate 2–3kg per m² after aeration,¹ or the supplier bands of 2/4/6kg per m² for light, medium and heavy dressings.⁴ Spread it in small heaps across the lawn — the RHS describes the rate as about a shovelful at a time.¹
• Work it in. Use a lawn lute if you have one; the back of a rake or a stiff brush does the same job.¹²
• Check the finish. When you're done there should be no obvious clumps of dressing on the surface and the grass should be clearly visible.² If dressing is sitting on the surface in quantity, you've applied too much per square metre — the RHS advice is simply to apply less next pass.¹

Overseeding and Finishing

• Overseed now if the lawn is thin. The scarified, aerated, freshly dressed surface is the best seedbed your lawn will offer all year. Sow at the overseeding rate from our grass seed calculator and keep the covering light — grass seed must not be buried.
• Water the lawn when you have finished — Rolawn's final touch to settle the dressing in.²
• Hold the mower. Don't mow immediately after dressing;² give the lawn a few days to grow up through it first.
• Feed as a separate job. Once the lawn is growing away, our lawn feed calculator works out spreader quantities for the season's feed.