Quick answer
To calculate mulch, multiply the bed area (length × width in feet) by the depth in feet, then divide by 27 for cubic yards. A 100 sq ft bed at 3 inches needs 25 cubic feet ÷ 27 = 0.93 cubic yards. Most bagged mulch is 2 cu ft, so that’s about 13 bags. One cubic yard covers 108 sq ft at 3 inches.
The mulch calculation formula
The formula for calculating mulch volume is:
Cubic yards = (Length × Width × Depth in feet) ÷ 27
Convert depth from inches to feet by dividing by 12 — a 3-inch mulch layer is 0.25 feet. The shortcut: cubic yards = square feet × depth (inches) ÷ 324. For 100 sq ft at 3 inches: 100 × 3 ÷ 324 = 0.93 cubic yards.
How deep should mulch be?
The right mulch depth depends on the purpose:
| Use | Recommended depth | Notes |
|---|---|---|
| Flower beds | 2–3 in | Suppresses weeds, retains moisture |
| Around trees | 2–3 in | Keep 3–6 in from trunk |
| Garden paths | 3–4 in | Bark or wood chips |
| New beds (first layer) | 3–4 in | Thicker to establish |
| Play areas | 6–12 in | Use engineered wood fiber |
| Slope erosion control | 3–4 in | Use shredded mulch that locks |
Thinner than 2 inches won’t suppress weeds effectively. Thicker than 4 inches can suffocate plant roots and trap too much moisture. Most landscape beds use 3 inches as a balance.
Mulch coverage per cubic yard
| Depth | Sq ft per cubic yard | Sq ft per 2 cu ft bag |
|---|---|---|
| 1 inch | 324 | 24 |
| 2 inches | 162 | 12 |
| 3 inches | 108 | 8 |
| 4 inches | 81 | 6 |
Coverage drops quickly as depth increases — doubling the depth halves the area. One cubic yard at 3 inches covers 108 sq ft; at 6 inches it covers only 54 sq ft.
How to calculate mulch for a circle
For round beds, use the circle formula: cubic yards = (π × radius² × depth in feet) ÷ 27. A 10-foot-diameter tree ring (5 ft radius) at 3 inches: π × 25 × 0.25 = 19.6 cubic feet ÷ 27 = 0.73 cubic yards.
For irregular beds, break the area into rectangles and circles, calculate each, and add the results.
Bagged mulch vs. bulk delivery
| Option | Cost | Best for |
|---|---|---|
| Bagged (2 cu ft) | $4–$8/bag ($54–$108/cu yd) | Small beds, DIY |
| Bulk delivery | $20–$50/cu yd + $50–$150 delivery | Beds > 3 cu yd |
| Bulk (by yard) | $25–$45/cu yd | Large landscaping |
Example: A 200 sq ft bed at 3 inches needs 1.85 cubic yards. Bagged: 25 bags at $5 = $125. Bulk: 1.85 cu yd at $30 = $56 + $75 delivery = $131. For larger projects, bulk wins — 5 cubic yards bagged costs $338 vs. $225 bulk delivered.
Frequently asked questions
Related calculators
For the volume math behind mulch, use the cubic yard calculator. For the area of a bed, try the square footage calculator. For converting square feet to cubic yards, see the square feet to cubic yards converter.