Soil and Compost Calculator
Work out the volume of soil or compost you need, in litres and m³. Digging out instead? See how much soil (or dirt) to clear, and which skips take soil.
Measure your project
Your answer
That covers 6 m².
If you buy bulk bags
Rolawn digs a new layer of soil improver in to 200 mm deep.
What it costs
Rolawn Soil Improver: £109.99 for 500 litres, £139.99 for 750, with VAT (Oct 2026). One seller, so treat it as a guide.
Quick answers
- Compost per m²
- A 50 mm layer of compost takes 50 litres for each m² of bed.
- Compost on beds you have
- The RHS digs in 5–10 kg per m². That is about half to one 15 litre bucket.
- Compost for a new bed
- Rolawn spreads 30–75 mm, by soil type, then digs it in to 200 mm.
- Dug soil grows
- One digging firm adds 25–30% to the size of the hole. Two firms say clay can grow by up to 40%.
How to work it out
- Measure the bed or area in metres. Multiply length by width for m².
- Pick the depth in mm. m² × depth in mm = litres of soil or compost.
- Divide the litres by 1,000 to get the soil volume in m³.
- Divide the litres by your bag size, then round up.
- Digging out? Take the hole's m³ and add 25–30% (one firm), or up to 40% for clay.
Soil improver for a 3 × 2 m bed on clay:
3 × 2 m = 6 m²
6 × 75 mm = 450 litres = 0.45 m³
450 ÷ 500 = 0.9 → 1 bulk bag
Compost calculator: how much per m²
Compost, or soil improver, feeds the soil you have. How much you need depends on the job.
On beds you already have
The RHS digs in about 5–10 kg per m². That is half to one 15 litre bucket for each m². As a mulch on top, it lays at least 5 cm, about 50 litres per m².
A new bed, by soil type
| Soil | Layer | Per m² | 500 L bag covers | 750 L bag covers |
|---|---|---|---|---|
| Sandy | 30 mm | 30 litres | 16.7 m² | 25 m² |
| Chalky | 50 mm | 50 litres | 10 m² | 15 m² |
| Clay | 75 mm | 75 litres | 6.7 m² | 10 m² |
Spread the layer, then dig it in to 200 mm deep.
Rolawn's soil improver costs £109.99 for 500 litres, with VAT. Wickes had the same bag for £115 on sale (was £123).
Soil and compost for common bed sizes
Find the bed nearest yours. Soil is at 150 mm, the least Rolawn gives for a border. Compost is at Rolawn's depth for each soil type.
| Bed | Soil, 150 mm | Compost, sandy (30 mm) | Chalky (50 mm) | Clay (75 mm) |
|---|---|---|---|---|
| 1 × 1 m | 150 | 30 | 50 | 75 |
| 2 × 1 m | 300 | 60 | 100 | 150 |
| 3 × 1 m | 450 | 90 | 150 | 225 |
| 3 × 2 m | 900 | 180 | 300 | 450 |
| 4 × 2 m | 1,200 | 240 | 400 | 600 |
| 5 × 3 m | 2,250 | 450 | 750 | 1,125 |
Nothing extra for settling. A 500 litre bulk bag holds 500 litres.
Digging out: soil removal and skips
Soil takes up more room once it is dug. One digging firm adds 25–30% to the size of the hole. Two firms say clay can grow by up to 40%.
In home-size skips, SunSkips says 8 yards is the biggest for soil and rubble. L&S Waste says don't fill even that size with only soil or rubble. Rules vary, so ask yours. For skip sizes, weight limits and rules, see our cubic yard calculator.
To work out the m³ of your hole first, use our cubic metre calculator.
Topsoil, compost or dug soil?
- Topsoil: the top layer of soil, sold to fill beds and lawns. Bagged topsoil weighs about 800 kg per m³ (Wickes). See our topsoil calculator.
- Compost or soil improver: spread over soil and dug in. Rolawn's soil improver is a peat-free compost.
- Dug soil: what you take out of a hole. It fills more space than it did in the ground.
Questions people ask
How much soil improver for clay soil?
Rolawn spreads a 75 mm layer and digs it in to 200 mm deep. A 500 litre bag covers about 6.7 m² at that depth.
How do I work out soil in litres?
m² × depth in mm = litres. One m³ is 1,000 litres. Soil bags are sold by the litre, such as 25 litres or 500 litres.
How much compost do I need?
The RHS digs in 5–10 kg per m², about half to one 15 litre bucket. For a new bed, Rolawn spreads 30–75 mm, or 30–75 litres per m².
How much does soil grow when you dig it out?
One digging firm adds 25–30% for normal soil. Two firms say clay can grow by up to 40%. So 1 m³ of ground fills about 1.25–1.3 m³ (clay up to 1.4 m³).
Should I dig compost in or spread it on top?
The RHS gives both ways. Dig in about 5–10 kg per m², or spread at least 5 cm on top as a mulch. For better weed control, it lays 8 cm.
How much does dug soil weigh?
We have no UK weight for dug soil. Bagged topsoil weighs about 800 kg per m³ (Wickes), but dug soil can differ. Ask your skip firm about its weight limit.
Where our numbers come from
- Topsoil weight: Wickes 500 litre topsoil bag (about 400 kg)
- Rolawn: topsoil depth for lawns and borders
- Topsoil settling and 70:30 mix: Field Compost
- Topsoil bag prices: Wickes 25 L and 500 L bags
- Topsoil 25 L bag covers 0.5 m²: B&Q Verve
- Topsoil tested to BS 3882:2015: Rolawn Blended Loam
- Compost per m²: RHS organic matter guide
- Soil improver depth by soil type: Rolawn bulk bag
- Dug soil bulking 25–30% (clay 40%): The Mini Digger Guy
- Clay bulks up to 40% when dug: NWTH muck-away guide
- Skip sizes: L&S Waste Management skip guide
- Skip sizes and heavy-waste limit: SunSkips size guide
- Unit sizes: NIST Handbook 44, Appendix C (1 ft = 0.3048 m; 1 US gallon = 231 cubic inches)
Made by BuildersCount. Last checked 4 Oct 2026.
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