How the mulch calculator works
Mulch is bought by volume but spread by area, so the calculator multiplies the length of the bed by its width, then by the depth you want to lay. Depth is entered in centimetres or inches and converted to metres or feet before multiplying, which is where most hand calculations go wrong: 3 inches is 0.25 ft, not 0.3.
Mulch volume = length × width × depth × 1.10The extra 10% covers settling in the first weeks, bumps and hollows in the soil, and the mulch you tuck around plant crowns. The result is shown in cubic metres or cubic yards for a bulk order, and as a bag count for the size you choose: 50 L or 70 L bags are usual in Europe, 2 or 3 cubic foot bags in North America.
Worked example
A border 5 m long and 2 m wide covers 10 m². At a depth of 7.5 cm (0.075 m) it needs 10 × 0.075 = 0.75 m³, or 0.825 m³ once the 10% allowance is added. That is 825 litres, so 16.5 bags of 50 L – buy 17. The imperial version of a similar bed: 16 ft × 6.5 ft is 104 ft²; at 3 inches it takes 104 × 0.25 = 26 ft³, or 28.6 ft³ with the allowance. Divide by 27 and you get 1.06 cubic yards, or ten 3 cu ft bags.
How deep should mulch be?
| Where | Depth | Why |
|---|---|---|
| Annual and perennial beds | 5–7.5 cm (2–3 in) | Blocks light from weed seeds without smothering plants |
| Shrub borders, around trees | 7.5–10 cm (3–4 in) | Keeps roots cool; leave a gap around trunks |
| Bark or wood-chip paths | 7.5–10 cm (3–4 in) | Lay over permeable fabric so it mixes less with soil |
| Playground wood chips | 23–30 cm (9–12 in) | Needed depth depends on fall height; follow local playground standards |
| Compost as a top-dressing | 2.5–5 cm (1–2 in) | Worms pull it in within a season |
What one bag or load covers
| Quantity | At this depth | Covers |
|---|---|---|
| 50 L bag | 5 cm | 1 m² |
| 2 cu ft bag | 2 in | 12 ft² |
| 3 cu ft bag | 3 in | 12 ft² |
| 1 m³ bulk | 7.5 cm | 13.3 m² |
| 1 yd³ bulk | 3 in | 108 ft² |
Bagged mulch suits a few small beds. Past roughly 1 m³ or 1.5 yd³, bulk delivery from a landscape yard is usually cheaper per unit and saves a pile of plastic sacks: a cubic yard equals 13.5 bags of 2 cu ft, and a cubic metre equals 20 bags of 50 L.
Common mulching mistakes
- Volcano mulching. Heaping mulch against tree trunks keeps bark wet and invites rot and rodents. Pull it back so the root flare stays visible.
- Going too thick. More than about 10 cm (4 in) on beds can starve roots of air and keep clay soils soggy.
- Topping up blindly. Push a finger into last year's layer; if 5 cm is still there, enter only the difference as the depth.
- Mixing up bag units. A 2 cu ft bag holds about 57 L and a 3 cu ft bag about 85 L, so a European 50 L bag is the smallest of the common sizes.
- Mulching over perennial weeds. Mulch stops seedlings, but bindweed and couch grass grow straight through it. Dig them out first.
Frequently asked questions
How many bags of mulch do I need for a 10x10 area?
A 10 ft × 10 ft area at 3 inches deep needs 25 ft³, or about 27.5 ft³ with a 10% allowance. That is 14 bags of 2 cu ft or 10 bags of 3 cu ft.
How much area does a cubic yard of mulch cover?
One cubic yard covers 162 ft² at 2 inches, 108 ft² at 3 inches and 81 ft² at 4 inches.
How many 50 litre bags of mulch are in a cubic metre?
Twenty. At 5 cm deep each 50 L bag covers 1 m², so a cubic metre covers about 20 m².
Should I remove old mulch before adding new?
Only if it is matted, mouldy or already deeper than about 10 cm. Otherwise loosen it with a rake and top it up to a total of 5–7.5 cm.
Does mulch settle after spreading?
Fresh shredded bark and wood chips usually shrink by 10–20% as they settle and dry. The calculator adds 10%; for very fluffy material, spread slightly thicker.
Last reviewed: 2026-09-27 · How we calculate