Mulch calculator
Cubic yards and bags for a bed of any shape — rectangle, or several beds added together.
- Volume
- — ft³
- Bags needed
- —
- Estimated cost
- —
How the calculation works
yd³ = length × width × (depth ÷ 12) ÷ 27
Bags are the same volume divided by the bag size in cubic feet. Round up: a thin spot in the bed is where weeds win.
Worked example
A 20 × 4 ft bed at 3 inches: 80 ft² × 0.25 ft = 20 ft³ = 0.74 yd³. With 5% waste, 0.78 yd³. In 2 ft³ bags: 20 × 1.05 ÷ 2 = 10.5, so 11 bags.
How deep should mulch be?
| Bed type | Depth | Note |
|---|---|---|
| Annual beds | 2 in | Easy to refresh each year |
| Perennial beds | 3 in | Weed suppression without smothering crowns |
| Trees and shrubs | 3–4 in | Keep 2 in clear of the trunk |
| Erosion control on slope | 4 in | Use a heavier mulch that locks together |
Frequently asked
How many bags make a cubic yard?
13.5 bags of 2 ft³, or 9 bags of 3 ft³. Bulk delivery wins above roughly one cubic yard, once you account for the delivery fee.
Does mulch depth add up year over year?
It decomposes — roughly 1 inch per year in a warm climate. Measure the existing layer before ordering; topping up 1 inch is usually enough.
Can I put mulch against the house?
Leave 6 inches between mulch and siding. It keeps termites and moisture away from the structure.