Mulch is sold two ways — by the bag at the garden centre and by the cubic yard delivered — and the two are hard to compare without the volume. This calculator turns your bed area and chosen depth into cubic yards, cubic metres and bag counts, so you can price both routes honestly.
The formula
One useful anchor: a cubic yard spread 3 inches deep covers 108 ft² — a bed about 10 × 11 ft. At 2 inches it covers 162 ft²; at 4 inches, 81 ft². Depth is the whole game: most “I ran out of mulch” stories are a depth estimate that quietly doubled.
How deep should mulch be?
2–3 inches for ornamental beds — enough to suppress weeds and hold moisture without smothering roots. 3–4 inches around trees and shrubs (pulled back from the trunk — never mulch volcanoes). 1–2 inches is a top-up over last year's mulch, which has usually compacted and decomposed by about half. Under play equipment, 6–9 inches of loose wood chips is the safety standard, a different league entirely.
Worked example
A 10 ft × 10 ft bed at 3 inches deep: volume = 100 × 0.25 = 25 ft³ = 0.93 yd³. In standard 2 ft³ bags that is 12.5 → 13 bags. Double the depth to 6 inches and everything doubles — 26 bags — which is why bulk starts winning quickly.
How to use this tool
- Measure the beds — for several beds, either add their areas into the direct-area box or run each bed separately.
- Enter the depth you will actually spread after settling, not the fluffy depth in the bag.
- Pick the bag size from the packaging if you are buying bagged.
- Compare bags vs the cubic-yard figure; around 2 yd³, get a bulk quote.
- Add a small extra allowance for irregular beds and heavy settling.
Mulch math for odd-shaped beds
For circles, use the Square Footage Calculator with the circle shape to get the area, then type it into the direct-area box here. For long borders, length × average width is close enough — mulch is forgiving in a way concrete is not.