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).
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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