DIY Home CalcsMulch Calculator
Find out how much mulch, topsoil or compost to order for a garden bed. Enter the bed size and how deep you want the layer, and see the result in cubic yards for a bulk delivery or in bags for the garden center.
How the mulch calculation works
Mulch is sold by volume. Multiply the area of the bed in square feet by the depth in feet (inches ÷ 12) to get cubic feet. Divide by 27 for cubic yards, or by the bag size for the number of bags.
Worked example
A 20 ft × 4 ft bed along a fence, mulched 3 inches deep:
- Area: 80 sq ft.
- Volume: 80 × 3 ÷ 12 = 20 cu ft, or 0.74 cu yd.
- In 2 cu ft bags: 10 bags.
A ring around a tree with a 6 ft diameter is π × 3² ≈ 28.3 sq ft; at 3 in deep that is about 7.1 cu ft, or 4 bags.
Coverage of one cubic yard
| Depth | Area covered by 1 cu yd | Area covered by a 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 |
Mulching tips
- Top up, don't double up. Existing mulch breaks down by about an inch a year. Measure what is left and only add enough to bring the total back to 2–3 in.
- Avoid "mulch volcanoes". Pull mulch back 3–6 in from trunks so bark stays dry.
- Weed first. Mulch suppresses new weeds but rarely smothers established ones.
- Bulk deliveries settle. Freshly dumped mulch is fluffy; order a little extra (about 5–10%) if you are covering a large area.
- Laying gravel paths between beds? Use the gravel calculator, which converts volume into tons.
Frequently asked questions
How much area does a cubic yard of mulch cover?
One cubic yard covers about 324 sq ft at 1 inch deep, 162 sq ft at 2 inches, 108 sq ft at 3 inches and 81 sq ft at 4 inches.
How many bags of mulch are in a yard?
A cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft.
How deep should mulch be?
Most extension services recommend 2 to 3 inches for shredded or bark mulch, and up to 4 inches for coarse nuggets. Keep mulch a few inches away from tree trunks and plant stems; piling it against bark can cause rot.
Is bulk or bagged mulch cheaper?
Bulk mulch is usually cheaper per cubic yard once you need more than 2 or 3 yards, but delivery fees apply. Bags are easier for small beds, top-ups and places a truck can't reach.
Can I use this for topsoil or compost?
Yes. The volume math is the same for any loose material. Topsoil and compost are often spread 1 to 3 inches deep when top-dressing beds and 4 to 6 inches for new beds.