Quick answer
A standard 2 cubic foot bag of mulch covers about 12 square feet at 2 inches deep, 8 square feet at 3 inches, or 6 square feet at 4 inches. For a typical bed at 3 inches deep, divide the bed's square footage by 8 to get the number of 2 cu ft bags. A 100 sq ft bed needs about 13 bags.
The formula
Mulch is sold by volume, so you need to turn your bed into cubic feet:
- Area (sq ft) = length x width in feet. For a circle, use 3.14 x radius x radius.
- Volume (cu ft) = area x depth in inches / 12.
- Bags = volume / bag size in cu ft. Round up.
Example: a bed 20 ft long and 5 ft wide is 100 sq ft. At 3 inches deep that is 100 x 3 / 12 = 25 cu ft. With 2 cu ft bags you need 25 / 2 = 12.5, so buy 13 bags. The mulch calculator does this math for rectangles, circles and known areas, and adds a waste allowance.
Coverage chart by depth and bag size
Square feet covered per bag. Bulk cubic yard included for comparison (1 cu yd = 27 cu ft).
| Depth | 1.5 cu ft bag | 2 cu ft bag | 3 cu ft bag | 1 cubic yard |
|---|---|---|---|---|
| 1 in | 18 sq ft | 24 sq ft | 36 sq ft | 324 sq ft |
| 2 in | 9 sq ft | 12 sq ft | 18 sq ft | 162 sq ft |
| 3 in | 6 sq ft | 8 sq ft | 12 sq ft | 108 sq ft |
| 4 in | 4.5 sq ft | 6 sq ft | 9 sq ft | 81 sq ft |
To use the chart, divide your bed area by the number in the matching cell. A 150 sq ft bed at 2 inches with 2 cu ft bags: 150 / 12 = 12.5, so 13 bags.
How deep should mulch be?
- New beds or bare soil: 2 to 3 inches of wood mulch is the common recommendation. It is deep enough to block light from most weed seeds without starving roots of air.
- Refreshing an existing bed: if 1 to 2 inches of old mulch remains, add about 1 inch. Measure the old layer with a trowel before you buy. Topping up to a full 3 inches every year builds an overly thick layer.
- Paths and play areas: wood chips are often laid 3 to 4 inches deep on paths. Playground safety guidance calls for much deeper loose fill, often 9 to 12 inches, which is a different calculation.
- Fine or shredded mulch packs down more than coarse chips, so stay near the low end. Coarse nuggets can go a little deeper.
Keep mulch 2 to 3 inches away from tree trunks and plant stems. Mulch piled against bark holds moisture against it and invites rot and pests.
Common reasons people run short
Guessing the area
Curved beds are hard to eyeball. Break an irregular bed into rough rectangles and circles, measure each and add them. If a bed wraps around a house corner, measure each leg separately.
Ignoring settling
Bagged mulch is often compressed in the bag and fluffs up when spread, but fresh shredded mulch also settles after the first rains. Most people add 5 to 10 percent extra to cover uneven ground and settling.
Mixing up bag sizes
Most store mulch comes in 2 cu ft bags, but 1.5 cu ft and 3 cu ft bags are common too, and some soil products come in 0.75 or 1 cu ft. Check the bag label for the cubic feet number, not the weight. Wet mulch is heavier but does not cover more ground.
Worked examples
| Project | Area | Depth | 2 cu ft bags |
|---|---|---|---|
| Ring around a tree, 6 ft across | about 28 sq ft | 3 in | 4 |
| Foundation bed, 40 x 4 ft | 160 sq ft | 3 in | 20 |
| Front beds totaling 300 sq ft | 300 sq ft | 2 in | 25 |
| Refresh of 300 sq ft | 300 sq ft | 1 in | 13 |
The tree ring uses radius 3 ft: 3.14 x 3 x 3 is about 28 sq ft. If the tree trunk is large, subtract its footprint.
When bulk makes more sense
One cubic yard equals 13.5 two-cubic-foot bags. Once a job passes about 2 to 4 cubic yards (roughly 27 to 54 bags), bulk delivery is often cheaper and saves a lot of hauling and plastic. The break-even depends on local bag and delivery prices: divide the delivery fee by how much you save per cubic yard, and if your job is bigger than that number, bulk is cheaper.
Spreading tips
- Pull weeds and edge the bed first. Mulch slows new weeds but does not kill established ones.
- Water dry soil before mulching so the mulch does not lock in dry conditions.
- Drop bags evenly around the bed so you are not carrying them far, then cut them open on the ground.
- Spread with your hands or a hard rake, then check depth in a few spots with a ruler.
- Pull mulch back from trunks, stems and house siding. Many pest guides suggest leaving a few inches of bare ground next to the foundation.
If you also need soil or compost under the mulch, the compost calculator uses the same area and depth math.