Mulch Calculator
Cubic metres and bags of mulch or bark for your beds and borders.
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About this calculator
Mulch and bark are sold in litres, gardens are measured in square metres — and the difference between a useful 7cm layer and a decorative sprinkle is the whole benefit. This calculator converts bed area and depth into cubic metres and 50-litre bags.
The formula
Volume (m³) = Area × (Depth ÷ 100)
Bags = Volume × 1000 ÷ 50
Worked example
12 m² of beds at 7cm: 0.84 m³ = 17 bags of 50L.
Common mistakes
- Piling mulch against plant stems and tree trunks, which causes rot — leave a gap.
- Spreading less than 5cm, which neither suppresses weeds nor holds moisture.
- Mulching over established weeds instead of clearing first.
Frequently asked questions
5–8cm for weed suppression and moisture retention. Refresh annually as it breaks down.
Above ~1 m³, loose or dumpy-bag deliveries beat 50L bags on price significantly.
Spring, after the soil has warmed and while it's moist — you lock in the moisture below.
Assumptions & limitations
Even coverage; bag size 50 litres (check yours — 60L, 70L and 100L bags exist).
Sources & verification
- Supplier bulk-bag coverage data — Coverage per bag depends on product density; supplier figures govern
All sources last accessed 24 July 2026.
Formula last verified: 24 July 2026
Maintained by: Steve Davis, Founder & Editor — see our editorial standards
Spotted an error or an out-of-date figure? Report it — corrections are prioritised over all other work (see our corrections policy).
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