How Much Mulch Do I Need?
Published 2026-09-04
Multiply the bed area in square feet by the depth in feet, then divide by 27 for cubic yards. At the standard 3-inch depth, one cubic yard covers about 108 square feet. A 200 square foot bed needs just under 2 cubic yards.
Mulch is bought two ways — by the bag in cubic feet, by the truckload in cubic yards — and the two are hard to compare until you have worked out the volume. Here is the whole calculation.
The formula
cubic feet = area ft² × (depth in ÷ 12)
cubic yards = cubic feet ÷ 27
bags (2 ft³) = cubic feet ÷ 2Coverage per cubic yard
A cubic yard is always 27 cubic feet, so how far it goes depends entirely on depth:
| Depth | Coverage per yd³ | Bags (2 ft³) per 100 ft² |
|---|---|---|
| 1 in | 324 ft² | 4.2 |
| 2 in | 162 ft² | 8.3 |
| 3 in | 108 ft² | 12.5 |
| 4 in | 81 ft² | 16.7 |
| 6 in | 54 ft² | 25 |
Change any measurement to update your estimate.
- Cubic feet
- 25 ft³
- 2 ft³ bags
- 13 bags
Worked example: beds around a house
| Bed | Dimensions | Area |
|---|---|---|
| Front foundation | 40 × 4 | 160 ft² |
| Side path border | 25 × 3 | 75 ft² |
| Island bed | 12 × 8 | 96 ft² |
| Total | 331 ft² |
At 3 inches:
- Depth in feet: 3 ÷ 12 = 0.25
- Cubic feet: 331 × 0.25 = 83 ft³
- Cubic yards: 83 ÷ 27 = 3.1 yd³
- Or bags: 83 ÷ 2 = 42 bags
How deep, and when not to
Three inches is the working default: deep enough to block light from weed seeds, thin enough that water and air still reach the roots. Oregon State University Extension’s Mulching Woody Ornamentals with Organic Materials puts arborist wood chips at 3–4 inches and screened bark at 3. Adjust from there:
- 2 inches for fine-textured mulch, which packs tighter and can suffocate roots at 3
- 3 inches for standard shredded hardwood or bark
- 4 inches for coarse chips, or in a bed you want to re-mulch less often
- Never pile it against a trunk. The same OSU publication says to avoid piling mulch immediately next to the trunk: it keeps the bark wet, raising the risk of fungal and bacterial disease, and gives voles cover to chew on it. Pull it back 3 inches from every stem.
Existing mulch counts. If a bed still has 1.5 inches of good mulch, you are topping up 1.5 inches, not laying 3.
Need it in other units? The mulch calculator converts the same measurements to bags, and cubic yards covers bulk deliveries of anything else.
Bags or bulk
Bagged mulch is normally 2 ft³, so 13.5 bags make a cubic yard. Bulk is cheaper per yard almost everywhere, and the crossover is usually around 6–8 bags — beyond that, the bag premium and the trips to the store outweigh the convenience.
Bulk arrives as a pile on your driveway with no bags to dispose of, but you need a place to put it and a way to move it. A cubic yard of hardwood mulch weighs roughly 400–800 lb depending on how wet it is, which is 8–12 wheelbarrow loads.
Order a little over
A bed edge is never a clean rectangle, and settling costs you depth within a few weeks. Measure to the widest point of each bed and round up to the next quarter yard. Leftover mulch keeps fine in a pile; a bed that is 20 square feet short looks unfinished all season.