Mulch is sold in cubic yards (bulk delivery) or cubic-foot bags (retail). The formula is: cubic yards = area (sq ft) × depth (in) ÷ 12 ÷ 27. At 3 inches deep over 200 sq ft, you need about 1.85 cubic yards — or 25 standard 2-cubic-foot bags. This calculator also works for topsoil, compost, and gravel.
The formula
cubic feet = area_sqft × depth_in ÷ 12
cubic yards = cubic_feet ÷ 27
bags (2 cu ft) = ceil(cubic_feet ÷ 2)
bags (3 cu ft) = ceil(cubic_feet ÷ 3)
Bags are rounded up with ceil() because you can't buy a fraction of a bag.
Practical examples
Example 1: 3-inch mulch layer over a 300 sq ft garden bed 300 × 3 ÷ 12 ÷ 27 = 2.78 cu yd (bulk), or 42 bags at 2 cu ft each
Example 2: Topping up 2 inches of mulch over a 500 sq ft area 500 × 2 ÷ 12 ÷ 27 = 3.09 cu yd (bulk), or 42 bags at 2 cu ft
Example 3: How much does 1 cubic yard of mulch cover at 3 inches? 1 cu yd = 27 cu ft × 12 ÷ 3 = 108 sq ft at 3 inches deep
Common mistakes
Ordering cubic feet instead of cubic yards from a bulk supplier. Bulk mulch is quoted in cubic yards; bagged mulch is in cubic feet. 1 cubic yard = 27 cubic feet, not 3. Confusing these leads to ordering far too little or too much.
Piling mulch against plant stems or tree trunks. A "mulch volcano" (thick mulch banked against a trunk) traps moisture and promotes rot. Keep mulch 2–3 inches away from trunks and crowns; depth recommendations apply to the open ground between plants.
Not accounting for compaction. Mulch settles 10–25% over its first season. If topping up an existing layer, measure the actual remaining depth and subtract from your target depth before calculating — don't assume the original application depth is still in place.
International and regional variations
| Material | Recommended depth | Notes |
|---|---|---|
| Wood chip / bark mulch | 2–3 in (5–8 cm) | Most common; decomposes slowly |
| Straw or hay mulch | 3–4 in (8–10 cm) | Lightweight; may contain weed seeds |
| Shredded leaves | 2–4 in (5–10 cm) | Free; decomposes to add nutrients |
| Gravel / decorative stone | 2–3 in (5–8 cm) | Permanent; does not decompose |
| Topsoil or compost | 1–2 in (2.5–5 cm) | Amends soil; use same volume formula |
Quick reference
| Area (sq ft) | Depth | Cubic yards | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|---|
| 100 | 2 in | 0.62 | 9 | 6 |
| 100 | 3 in | 0.93 | 13 | 9 |
| 200 | 3 in | 1.85 | 25 | 17 |
| 500 | 3 in | 4.63 | 63 | 42 |
| 1,000 | 3 in | 9.26 | 125 | 84 |