A 10 × 10 garden bed is the most common mulch job. The answer changes with depth, so here is the normal 3-inch depth first, then the other depths in the table.
For a 10 × 10 bed at 3 inches deep: 0.93 cubic yards of mulch, or 13 bags of the common 2 cubic feet size.
Step 1: Volume 10 ft × 10 ft × (3 ÷ 12) ft = 25 cubic feet. Depth is in inches, so divide by 12 first.
Step 2: Cubic yards 25 ÷ 27 = 0.93 cubic yards. That is the amount for bulk delivery.
Step 3: Bags one bag holds 2 cubic feet. 25 ÷ 2 = 12.5, and bags are sold whole, so 13 bags.
The same 10 × 10 bed at different depths:
| Depth | Cubic yards | Bags (2 cu ft) |
|---|---|---|
| 2 inches | 0.62 yd³ | 9 bags |
| 3 inches | 0.93 yd³ | 13 bags |
| 4 inches | 1.23 yd³ | 17 bags |
Other bed sizes at 3 inches deep: 5 × 10 ft = 0.46 yd³ / 7 bags · 10 × 20 ft = 1.85 yd³ / 25 bags · 20 × 20 ft = 3.70 yd³ / 50 bags.
2–3 inches for most beds. Less than 2 lets weeds through; more than 4 can keep water and air from the roots.
One 2 cu ft bag covers about 8 sq ft at 3 inches deep, 12 sq ft at 2 inches, 6 sq ft at 4 inches.
Under about 1 cubic yard, bags are simpler. Over 2 yards, bulk is usually much cheaper per yard, but you need a place for the truck to dump it.