Mulch Calculator
Enter the size of your garden bed and mulch depth in millimetres to get cubic metres, litres and the number of 70 L bags – and whether bulk is cheaper.
Formulas shown on this page · Last reviewed October 2026
How the mulch calculator works
volume (m³) = area (m²) × depth (mm) ÷ 1,000
litres = volume × 1,000
bags = litres × (1 + waste) ÷ bag size (L)
For a circular bed or tree ring, the area is π × (diameter ÷ 2)². One cubic metre is 1,000 litres, so a 70 L bag covers about 0.93 m² at 75 mm deep.
How deep should mulch be?
| Use | Depth |
|---|---|
| Flower beds and borders | 50–75 mm |
| Around shrubs and trees | 75–100 mm |
| Vegetable garden (fine mulch) | 50 mm |
| Weed suppression on paths | 75–100 mm |
Buying mulch in the UK
Popular choices include bark chippings, wood chip and composted bark. Garden centres sell bags of about 50–80 L, while bulk bags and loose loads of bark are cheaper for large borders. A spring layer over damp soil suppresses weeds and holds moisture through dry spells; top up in autumn as bark breaks down.
At the default prices, bagged mulch costs about £86 per cubic metre (£6.00 per 70 L bag) compared with roughly £45 per m³ in bulk before delivery. Bulk wins for beds over about 1 m³. These are typical prices – check your local supplier.
Frequently asked questions
How much mulch do I need for a 6 × 2 m bed at 75 mm deep?
The base volume is 0.9 m³ (900 L). With 5% extra, order 0.95 m³ – about 945 L.
How many 70 L bags is that?
945 L ÷ 70 L = 14 bags (rounded up), costing about £84 versus £43 in bulk.
How many square metres does one cubic metre of mulch cover?
At 75 mm deep, 1 m³ covers about 13.3 m². At 50 mm it covers 20 m².
Should I keep mulch away from trunks and stems?
Yes. Leave a small gap around trunks and plant stems so moisture does not sit against the bark and cause rot.