Mulch Calculator (Metric)
Find how much mulch you need in cubic metres and 56 L bags from your bed size in metres and the depth in centimetres you want.
What your result means
Mulch needed is the volume to fill your bed at the chosen depth, in cubic metres (how bulk mulch is sold). Bags is the count of standard 56 L bags. Bulk by the cubic metre is cheaper once you need more than about a dozen bags. Need the bed area first? Use our area calculator.
How to use this calculator
- Measure the bed length and width in metres.
- Pick a depth — 5 to 8 cm is standard for most beds.
- Read the cubic metres and bag count.
- Order by the cubic metre if you need more than a dozen bags.
- For odd beds, split into rectangles and add the areas.
The formula
Depth converts from centimetres to metres by dividing by 100. Length times width times that depth gives cubic metres. A standard mulch bag holds 56 litres, about 0.0566 m³.
Worked example
A 6 by 4 m bed is 24 m². At 8 cm deep that's 1.92 m³ of mulch, about 34 of the 56 L bags. Past a dozen bags, bulk by the cubic metre is cheaper.
Mulch depth guide
| Use | Recommended depth |
|---|---|
| Annual flower beds | 2 – 5 cm |
| Shrub & perennial beds | 5 – 8 cm |
| Around trees | 8 – 10 cm (not on trunk) |
| Weed suppression | 8 cm |
| Bag size | 56 L per bag |
Tips & gotchas
- Don't pile mulch against trunks or stems — keep a few centimetres clear to prevent rot.
- Bulk mulch by the cubic metre beats bags once you pass roughly a dozen bags.
- One cubic metre covers about 12 m² at 8 cm deep.
- Refresh, don't rebuild — top up existing beds a couple of centimetres rather than piling on.
- Order about 5% extra to cover settling and uneven ground.
Frequently asked questions
How much mulch do I need?
Multiply bed area by depth in metres for cubic metres. A 24 m² bed at 8 cm needs about 1.92 m³.
How many bags of mulch in a cubic metre?
About 18 bags, since a cubic metre is 1,000 litres and standard bags hold 56 litres each.
How deep should mulch be?
5 to 8 cm for most beds. Too thin won't suppress weeds; too thick can suffocate roots and hold excess moisture.
Should I buy bags or bulk?
Bags suit small beds. Once you need more than about a dozen, bulk by the cubic metre is cheaper and less hauling.
How much area does a cubic metre of mulch cover?
About 12 m² at 8 cm deep, or roughly 20 m² at 5 cm.
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Estimates only — see our full disclaimer.