Mulch & Soil Volume Calculator
Set the bed shape and size, the depth you want to spread, the material and the bag size. The page returns the area covered, cubic metres, litres, how many bags to buy, the weight to carry and the depth you entered.
Mulch is sold by the litre in bags and by the cubic metre in bulk, but beds are measured in square metres and depth in centimetres. Pick the shape, enter two numbers, and the page converts everything into bags and kilos.
The bed and the material
Measure the bed in metres. Depth is the loose depth after settling, not the depth of the bag.
Area covered
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Volume
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Litres
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Bags to buy
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Weight
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Depth
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How this was worked out
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Density and where each material belongs
| Material | Density | Best used for |
|---|---|---|
| Bark mulch — 250 kg/m³ | 250 kg/m³ | Borders and shrub beds: holds moisture, looks tidy, breaks down slowly |
| Compost — 500 kg/m³ | 500 kg/m³ | Digging into tired soil: feeds the bed rather than just covering it |
| Wood chips — 300 kg/m³ | 300 kg/m³ | Paths and tree pits: cheap, long lasting, fine on bare ground |
| Gravel — 1500 kg/m³ | 1500 kg/m³ | Drainage strips and decorative tops: heavy, permanent, not for digging in |
Quick volume by bed area
| Area | 5 cm | 7.5 cm | 10 cm | 50 L bags at 10 cm |
|---|---|---|---|---|
| 10 m² | 0.5 m³ | 0.75 m³ | 1.0 m³ | 20 |
| 20 m² | 1.0 m³ | 1.5 m³ | 2.0 m³ | 40 |
| 50 m² | 2.5 m³ | 3.75 m³ | 5.0 m³ | 100 |
| 100 m² | 5.0 m³ | 7.5 m³ | 10.0 m³ | 200 |
Five rules before you order
- One cubic metre is 1000 litres. Bags are labelled in litres, bulk loads in cubic metres, so convert before comparing prices.
- A 50 litre bag is about 0.05 m³, so roughly 20 bags make one cubic metre. Smaller 40 litre bags need 25.
- Spread 5 cm to top up an existing bed, 7.5 cm for a new bed, and no more than 10 cm even where you are suppressing weeds.
- Keep mulch about 5 cm clear of trunks and stems. Piled against bark it traps moisture and invites rot.
- Above about 3 m³, bulk by the cubic metre is usually cheaper than bags, even after delivery. Check the delivery fee first.
Practical notes
- Water the bed before spreading and again after. Dry mulch on dry soil sheds water instead of letting it through.
- Rake to an even depth rather than heaping around plants; uneven depth is where weeds get through.
- Fresh wood chips pull nitrogen from the topsoil as they break down. Keep them on paths, or add a nitrogen feed.
- Write the delivery date on the bag. Bulk mulch stored in a wet heap for weeks can sour and mat.
Four common mistakes
- Confusing cubic metres with litres. Ordering 20 m³ when you meant 20 bags is a very expensive morning.
- Measuring depth in the bag rather than on the bed. A 50 litre bag does not cover 1 m² at 5 cm.
- Piling mulch into a cone against the trunk. Roots suffocate and the bark stays wet.
- Buying bags for a large bed. Twenty small bags cost far more than one bulk load and take all afternoon to open.
Volumes are geometric estimates, not a substitute for the product label. Over-mulching can smother roots, and uncomposted material can damage young plants — follow the supplier instructions and keep mulch clear of stems.