Worked example: 3 inches deep
| Step | Math | Result |
|---|---|---|
| Area | 20 ft × 20 ft | 400 sq ft |
| Volume at 3 in | 400 × 3 ÷ 12 | 100.0 ft³ |
| Add 5% extra | 100.0 × 1.05 | 105.0 ft³ |
| Cubic yards | 105.0 ÷ 27 | 3.89 yd³ |
| 2 ft³ bags | 105.0 ÷ 2, rounded up | 53 bags |
| 3 ft³ bags | 105.0 ÷ 3, rounded up | 35 bags |
Mulch by depth
| Depth | Cubic feet | Cubic yards (+5%) | 2 ft³ bags | Bag cost | Bulk order (yd³) | Bulk delivered | Cheaper |
|---|---|---|---|---|---|---|---|
| 2 in | 66.7 | 2.59 | 35 | $140 | 3.0 | $195 | Bags |
| 3 in | 100.0 | 3.89 | 53 | $212 | 4.0 | $235 | Bags |
| 4 in | 133.3 | 5.19 | 70 | $280 | 5.5 | $295 | Bags |
At 3 inches, bags win: 53 bags cost about $212 versus $235 for a delivered 4.0 yd³ (which includes a $75 delivery fee).
Prices used: 2 ft³ bag $4, 3 ft³ bag $6; bulk mulch $40/yd³ plus $75 delivery (1 yd³ minimum). Spring sales change the crossover.
Top-ups and depth
If the bed already has mulch, a 1 inch refresh takes only 1.30 yd³ or 18 bags of 2 ft³. Keep mulch 2–3 inches away from trunks and stems.
Nearby sizes
Also see 12×12 bed , 10×20 bed, or the mulch by bed size chart. Use the mulch calculator for other sizes.