Garden & outdoor
How much soil or mulch do you need (in bags)?
Liters, cubic meters and 50 L bags of topsoil, compost or mulch for beds and planters, from area and depth.
Quick answer
Soil and mulch are sold by the bag but needed by volume, and the conversion trips everyone up at the garden centre. The formula is simple: area × depth = volume, so 10 m² covered with 7 cm of bark mulch is 0.7 m³ — that’s 700 litres, or fourteen 50 L bags. The calculator adds 10% because loose material settles and compacts once spread and watered.
Volume needed
770 L (0.77 m³)
- In 50 L bags
- 16 bags
- In 20 L bags
- 39 bags
Volume = area × depth, plus 10% for settling and compaction. Recommended depths: 5-10 cm for bark mulch (less lets weeds through), 3-5 cm for compost worked into beds, 10+ cm for topsoil in new beds or planters. For gravel, one 25 kg bag covers roughly 15 L of volume.
How it works
Depth is where the real decisions are. Bark mulch needs 5-10 cm to actually suppress weeds — a thin decorative sprinkle does nothing but look good for a month. Compost worked into beds needs only 3-5 cm. Topsoil for new beds or planters wants 10 cm or more. One warning born of experience: keep mulch a few centimetres away from plant stems and tree trunks — piled against bark it traps moisture and invites rot and rodents.
Frequently asked questions
How many bags of mulch do I need for 10 m²?+
At the recommended 7 cm depth, 10 m² needs about 770 litres including settling — sixteen 50 L bags, or eleven 70 L bags. If you’re only refreshing an existing layer, 3-4 cm (around 8 bags of 50 L) is enough. For areas above 30 m², loose material delivered by the cubic metre is usually much cheaper than bags.
Should I put weed fabric under mulch?+
Under gravel and stone: yes, always — it stops the stone sinking into the soil and weeds coming up. Under organic bark mulch: opinions differ. The fabric blocks weeds initially, but it also stops the mulch enriching the soil as it decomposes, and after 2-3 years weeds germinate in the decomposed layer on top of the fabric anyway. A thick 8-10 cm mulch layer alone controls weeds almost as well.
How many liters is a cubic meter of soil?+
1 m³ = 1,000 litres, so twenty 50 L bags. Weight varies with moisture: a cubic metre of topsoil weighs roughly 800-1,200 kg, bark mulch only 250-400 kg. That weight difference is why mulch is pleasant to spread and topsoil deliveries need to go exactly where you want them the first time.
How much soil do I need for a raised bed?+
Multiply length × width × height: a classic 2 × 1 m bed, 30 cm high, holds 600 litres — twelve 50 L bags. To save money, fill the bottom third with branches, leaves and coarse compost (the "hugelkultur lite" approach) and use quality soil only for the top 20 cm where roots actually feed.
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