How to calculate how much mulch you need
Mulch is sold by volume: in bulk by the cubic yard, and in bags measured in cubic feet. To find the volume you need, multiply the area of your beds by the depth of the mulch layer.
Cubic feet = length (ft) × width (ft) × depth (ft)
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size (round up)
Convert the depth from inches to feet by dividing by 12, so 3 inches is 0.25 ft. A round bed or tree ring uses π × radius² for the area; a triangular corner bed uses base × height ÷ 2. When a project has several beds, calculate each one separately and add them up. A 5% allowance, which the calculator includes by default, covers uneven ground and spillage.
Example: a 20 ft × 4 ft border at 3 inches deep
- Area: 20 × 4 = 80 sq ft
- Volume: 80 × 0.25 = 20 cubic feet = 0.741 cubic yards
- With 5% extra: 21 cubic feet = 0.778 cubic yards
- Bags: 11 two-cubic-foot bags, or 21 one-cubic-foot bags
How deep should mulch be?
A layer of 2 to 3 inches is the usual recommendation for garden beds and around shrubs. Less than 2 inches allows weeds through, and more than 3 to 4 inches can hold too much moisture and starve roots of air. Around trees, spread mulch in a wide ring but keep it a few inches away from the trunk rather than piling it against the bark. Refresh the layer each year or two as it breaks down, topping up rather than starting from scratch. The table shows how far mulch goes at each depth.
| Depth | Sq ft covered by 1 cubic yard | Sq ft covered by one 2 cu ft bag |
|---|---|---|
| 1 in | 324 | 24 |
| 2 in | 162 | 12 |
| 3 in | 108 | 8 |
| 4 in | 81 | 6 |
Bags or bulk mulch?
One cubic yard equals 13.5 two-cubic-foot bags, so a project that needs several yards means dozens of bags to carry, open and dispose of. Bags suit small beds, containers and top-ups. For anything larger, ask local landscape suppliers for a bulk delivery price per cubic yard and compare it with the bag price multiplied by 13.5. Delivery fees and minimum quantities vary, so get a quote before you decide. Bulk mulch is also easier to spread with a wheelbarrow from one pile.
Mulch weight varies a great deal with the material and how wet it is, so it is not shown here. If you are also building up the bed, calculate the soil with the topsoil calculator, add stone paths with the gravel calculator, or measure any other volume with the cubic yard calculator.
Frequently asked questions
How much mulch do I need for 100 square feet at 3 inches deep?
You need 25 cubic feet, which is 0.926 cubic yards, or 13 two-cubic-foot bags (12.5 rounded up). Add about 5% if your ground is uneven.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet: 13.5 two-cubic-foot bags (round up to 14), 27 one-cubic-foot bags, or 54 half-cubic-foot bags.
How thick should a layer of mulch be?
About 2 to 3 inches suits most garden beds. Keep mulch a few inches clear of tree trunks and plant stems to prevent rot.
How much does a cubic yard of mulch cover?
A cubic yard covers 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.
Is it cheaper to buy mulch in bulk?
Usually yes once you need a few cubic yards, but delivery charges and minimum orders apply. Compare the bulk price per cubic yard with the bag price multiplied by 13.5 for 2 cubic foot bags.
More free calculators
These calculators give estimates for planning only. Densities, bag sizes and coverage vary by supplier, so confirm quantities before you order.