Compost calculator
Topdressing beds, reviving a lawn, or mixing your own soil — enter the area and depth of compost to get yards, bags and weight.
Result
Compost needed
How much compost do I need?
Formula
ft³ = area (ft²) × depth (in) ÷ 12 · yd³ = ft³ ÷ 27 · tons ≈ yd³ × 0.55
Example: topdressing a 20 × 10 ft bed with 1 inch of compost: 200 × 1/12 = 16.7 ft³ = 0.62 yd³ (about 17 of the 1 ft³ bags, or a half-yard scoop bulk).
How deep to apply compost
| Use | Depth | Note |
|---|---|---|
| Lawn topdressing | ¼–½ in | Thicker smothers grass |
| Annual bed refresh | 1–2 in | Then mulch on top |
| New beds / heavy clay | 2–3 in tilled in | Mix into top 6–8 in |
| Compost as mulch | 2–3 in | Finer grades only |
Compost is not mulch. Finished compost feeds soil but also grows weeds and washes away. Feed the soil with compost, then cover it with 2–3 in of mulch — that's the combination extension services recommend.
Bulk compost ($30–50/yd³ delivered) beats bagged above about 10 bags. For filling raised beds, compost should be ⅓ or less of the mix, not the whole thing.
Frequently asked questions
How much compost for 1,000 square feet?
At 1 inch: 83 ft³ = 3.1 yd³ ≈ 1.7 tons. At ½ in for a lawn topdress: 1.5 yd³.
How many bags of compost is a yard?
A 40 lb compost bag is about 1 ft³, so 27 bags per yard. Bulk delivery wins above ~10 bags.
Can I use compost instead of mulch?
For a thin soil-feeding layer under mulch, yes. As a bare-surface mulch it crusts, hosts weeds and disappears into the soil in weeks — use wood mulch on top.
How much compost per tomato plant?
A shovelful (about 1–2 dry qt) worked into each planting hole, or 1–2 in across the bed pre-season.