Soil Amendment Calculator
Calculate how much compost, peat moss, or other amendments to add to improve your garden soil.
Amendment Needed
Soil amendments improve soil structure, drainage, water retention, and nutrient content.
How much to add:
Volume = Area × Depth of Amendment
Recommended amendment depths:
| Goal | Depth to Add |
|---|---|
| Light improvement | 1–2 inches (2.5–5 cm) |
| Standard garden bed prep | 3–4 inches (8–10 cm) |
| Heavy clay remediation | 4–6 inches (10–15 cm) |
| Raised bed fill | 6–12 inches (15–30 cm) |
Common amendments (imperial):
- Compost: ~1 cubic yard covers 108 sq ft at 3 inches deep
- Peat moss: 1 bale (3.8 cu ft) covers about 15 sq ft at 3 inches
- Perlite: Mix 10–20% by volume
- Gypsum: 40 lbs per 1,000 sq ft for clay soil
Common amendments (metric):
- Compost: ~1 cubic meter covers 10 sq m at 10 cm deep
- Peat moss: 1 bale (107 L) covers about 1.4 sq m at 8 cm
- Gypsum: 2 kg per 10 sq m for clay soil
Tips:
- Work amendments into the top 6–8 inches (15–20 cm) of soil
- Add amendments in fall for spring planting when possible
- Test soil pH before and after amending