Soil
Mulch Calculator
Work out cubic yards, bags, and cost of mulch for any bed shape and depth, with coverage guidance.
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Working out how much mulch you need
Mulch is sold by volume and applied by depth, which is why so many people under-order. The calculation is area multiplied by depth, with the depth converted to the same unit as the area. Three inches over 100 square feet is 25 cubic feet — a little under a cubic yard, or thirteen 2-cubic-foot bags.
The number that matters most is depth, and it is the one people guess at. Too shallow and weeds push straight through; too deep and you starve the soil surface of oxygen and encourage roots to grow up into the mulch layer where they dry out.
Coverage at a glance
| Depth | Coverage per cubic yard | Coverage per 2 cu ft bag |
|---|---|---|
| 1 in | 324 sq ft | 24 sq ft |
| 2 in | 162 sq ft | 12 sq ft |
| 3 in | 108 sq ft | 8 sq ft |
| 4 in | 81 sq ft | 6 sq ft |
Choosing the right mulch
| Mulch | Best depth | Lasts | Best for |
|---|---|---|---|
| Shredded hardwood bark | 3 in | 1-2 years | Shrub borders, slopes — it knits and resists washing |
| Bark chips or nuggets | 3 in | 2-3 years | Paths and low-traffic beds; floats in heavy rain |
| Wood chip (arborist) | 3-4 in | 1-2 years | Tree rings, woodland beds; often free locally |
| Compost | 1-2 in | 1 season | Vegetable beds — feeds as well as covers |
| Leaf mould | 2 in | 1 season | Woodland and perennial beds; excellent structure |
| Straw | 4-6 in | 1 season | Vegetable beds, strawberries; check it is seed-free |
| Gravel or slate | 2 in | Indefinite | Alpine, Mediterranean and drought planting |
How to apply it
- Weed thoroughly first. Mulch suppresses seedlings; it will not smother established perennial weeds like bindweed or couch grass.
- Water the ground if it is dry. Mulch slows evaporation but it also slows rewetting, so mulching over dry soil locks the drought in.
- Spread evenly to the target depth, working from the back of the bed forwards.
- Pull the mulch back an inch or two from the stems of herbaceous plants and several inches from tree and shrub trunks.
- Leave the root flare of every tree fully visible. If you cannot see the trunk widening at the base, there is too much mulch.
When to mulch
Mid to late spring is the classic timing: the soil has warmed, winter rain has recharged moisture, and you seal that moisture in before summer. Mulching too early in cold wet soil insulates it and delays warming, which slows everything you have just planted. An autumn mulch is worth applying on exposed beds to protect the surface structure over winter.
How many bags of mulch are in a cubic yard?
Thirteen and a half 2 cu ft bags, or eighteen 1.5 cu ft bags, make one cubic yard. A cubic yard covers about 108 sq ft at 3 inches deep.
How deep should mulch be?
Two to three inches for most beds, three to four for weed suppression on open ground, and one to two inches for fine mulches such as compost or leaf mould, which pack more densely.
Should mulch touch plant stems?
No. Pull mulch back an inch or two from the stems of perennials and several inches from tree trunks. Mulch held against bark keeps it wet and invites rot, borers, and rodents.
How often should mulch be replaced?
Organic mulches break down and need topping up annually or every other year. Rather than adding a full depth each time, measure what remains and top up to the target depth.
Last reviewed February 2026