How this calculator works
Multiply the area by the depth in metres to get cubic metres, then add an allowance for spreading and settling. Divide by the volume of a bag to get the number of bags (a 50 litre bag is 0.05 m³).
Worked example: a 4 × 3 m border (12 m²) mulched 50 mm deep: 12 × 0.05 = 0.6 m³, or 0.66 m³ with 10% extra. That is 14 bags of 50 litres (13.2 rounded up).
Bags of 50 litre bark by area and depth (10% extra)
Bags to buy for common areas.
| Area | 50 mm deep | 75 mm deep | 100 mm deep |
|---|---|---|---|
| 5 m² | 6 | 9 | 11 |
| 10 m² | 11 | 17 | 22 |
| 20 m² | 22 | 33 | 44 |
| 30 m² | 33 | 50 | 66 |
| 50 m² | 55 | 83 | 110 |
Tips before you buy
- Spread bark on weeded, damp soil, and keep it a few centimetres clear of the stems of plants and shrubs, so that the stems do not rot.
- For weed suppression, lay a membrane first, or put down newspaper or cardboard; a layer of 50 to 75 mm of bark does the job on its own for most weeds.
- Play areas need a deeper layer of a bark that is made for play surfaces, to a depth that meets the safety standard for the equipment. Ask the supplier.
- Do not use bark that is fresh from the tree on beds that are about to be planted: it can take nitrogen from the soil while it breaks down.
- Buy in bulk if you can. A loose load or bulk bag is far cheaper per m³ than small bags.
Tools & materials for this project
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Frequently asked questions
How much bark do I need for a 4m x 3m border?
About 0.66 m³ at 50 mm deep with 10% extra, which is 14 bags of 50 litres.
How many bags of bark make a cubic metre?
20 bags of 50 litres, about 14 bags of 70 litres, or 13 bags of 75 litres.
How deep should bark mulch be?
50 mm is usual for borders, and 75 mm for paths and where weeds are a problem. A deeper layer can stop air reaching the soil.
How often should I replace bark mulch?
Top it up every one to three years, as it rots down into the soil. Rake it over in spring to freshen it.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.