Plant Pot Soil Volume Calculator
Calculate potting soil volume for round, square, or rectangular pots.
Enter dimensions to get liters and quarts needed with a bags-to-buy estimate.
Potting soil volume calculation determines how many bags or liters of potting mix you need to fill one or more plant containers — accounting for pot shape, drainage layer, and proper fill level.
Core formulas:
Cylindrical pots: Volume = π × r² × h
Rectangular/square planters: Volume = Length × Width × Height
Tapered pots (frustum approximation): Volume ≈ h/3 × (r₁² + r₁×r₂ + r₂²) × π
Where r = radius (half the diameter), h = height, all in the same unit (inches or cm).
Conversion to useful units:
- Cubic inches → Liters: Cubic inches ÷ 61.02
- Cubic inches → Quarts: Cubic inches ÷ 57.75
- Cubic inches → US gallons: Cubic inches ÷ 231
Pot size to soil volume guide:
| Pot Diameter | Approximate Volume | Soil Needed |
|---|---|---|
| 4 inches | 0.5 quarts | Small herb pot |
| 6 inches | 1–2 quarts | Single herb/succulent |
| 8 inches | 2–3 quarts | Small annual |
| 10 inches | 3–5 quarts | Mid-size plant |
| 12 inches | 5–7 quarts | Standard container |
| 14 inches | 7–11 quarts | Large perennial |
| 16–18 inches | 12–18 quarts | Small shrub |
Important adjustments:
- Drainage layer: If you add 1–2 inches of gravel or perlite at the bottom, subtract that volume
- Fill to 1–2 inches below the rim to prevent overflow during watering
- Settling allowance: Add 10–15% extra — potting mix compacts after first watering
Worked example: A 12-inch diameter, 10-inch tall cylindrical pot. Volume = π × 6² × 10 = π × 360 = 1,131 cubic inches Liters = 1,131 ÷ 61.02 = 18.5 liters Quarts = 1,131 ÷ 57.75 = 19.6 quarts With 10% settling buffer: buy 21–22 quarts (~2 standard 10-quart bags).