Mulch comes in bags and in bulk, and both are measured in the same unit: cubic feet. Once you have the volume, the two ways of buying are just different divisions.
Volume (cu ft) = bed area (sq ft) × depth (ft)
Depth in feet = depth in inches ÷ 12
Bags = volume ÷ cu ft per bag, rounded up
Cubic yards = volume ÷ 27
A 20 × 10 ft bed, 3 inches deep
The bed is 200 sq ft. Three inches is 0.25 ft, so the volume is 50 cu ft. The depth here is an example, not advice about how deep your mulch should be; the depth guide covers how it changes the quantity.
Worked example 20 × 10 ft bed, 3 in deep, 2 cu ft bags
| Material | Calculated | Buy |
|---|---|---|
| Mulch3 in deep, no allowance | 25 bags | 25 × 2 cu ft bags |
The calculation gives 25 bags, and the list says 25 × 2 cu ft bags. For a bulk delivery of the same volume the planner shows 1.85 yd³ in bulk.
Bags to cubic yards
A cubic yard is 27 cu ft. With 2 cu ft bags that is 27 ÷ 2 = 13.5 bags per yard, so a bed of this size sits well above a yard of mulch. Bag sizes vary, and a 3 cu ft bag changes the count to 17 × 3 cu ft bags for the same bed.
This example assumes
- 2 cu ft bags (the planner also offers 1.5 and 3 cu ft, or a custom size)
- No extra allowance, the planner’s starting value for mulch
What changes the estimate?
- Mulch depth, which scales the volume directly
- Bag size printed on the bag, which varies by brand
- Bed area: curved beds are best measured as rectangles and circles added together
- Whether you want an allowance for settling or uneven edges
Check the bag
Retailers print the bag volume in cubic feet. Use that rather than the bag weight, since weight depends on how wet the mulch is.