Pot Size Calculator
Find the recommended pot diameter and soil volume for your plant type and mature size.
Supports inches/gallons and cm/liters.
Plant pot size and soil volume matching is critical for healthy plant growth. Too small a pot restricts roots and causes stress; too large a pot holds excess moisture and can cause root rot.
Pot volume formula (cylinder approximation): Volume = π × r² × h
Where:
- r = inner radius (half the inner diameter)
- h = inner height of the pot
Most pots are tapered (wider at top) — frustum volume formula: Volume = (π × h ÷ 3) × (R² + R×r + r²)
Where R = top inner radius, r = bottom inner radius, h = pot height.
Standard pot sizes and approximate soil volumes:
| Pot Diameter | Common Volume | Best For |
|---|---|---|
| 4 inches | 0.5 liters | Seedlings, herbs, small succulents |
| 6 inches | 1.5 liters | Small houseplants, herbs |
| 8 inches | 3.5 liters | Medium houseplants (pothos, peace lily) |
| 10 inches | 6–7 liters | Larger houseplants (philodendron, ficus) |
| 12 inches | 10–12 liters | Small shrubs, large houseplants |
| 14 inches | 15–18 liters | Medium shrubs, citrus trees |
| 16–18 inches | 25–40 liters | Large shrubs, fruit trees, bougainvillea |
| 24+ inches | 80+ liters | Small trees |
Repotting rule: Move up one pot size at a time — typically 2 inches larger in diameter (not doubling the pot size, which would hold too much water for the current root ball).
Soil type and drainage:
- Standard potting mix: 60% peat/coco coir + 30% perlite + 10% compost
- Succulents/cacti: 50% gritty sand or perlite + 50% regular mix
- Orchids: bark-based, very open structure — not regular soil
- One cubic foot bag of potting soil ≈ 28.3 liters
Cost of soil per pot (US average potting mix ~$8–$12 per cubic foot):
- 6-inch pot (1.5L): ~$0.50 of soil
- 10-inch pot (6L): ~$2.10 of soil
- 14-inch pot (17L): ~$6.00 of soil
- 24-inch pot (80L): ~$29 of soil
Worked example: You have a monstera in a 10-inch pot (6 liters) that’s root-bound. You’re moving it to a 12-inch pot (11 liters).
- Additional soil volume needed: 11 − 6 × (root ball fraction 0.6) = 11 − 3.6 = 7.4 liters of fresh potting mix
- That’s approximately 0.26 cubic feet — about one-third of a standard small bag
- Tip: refresh the bottom 3 inches with fresh mix, then center the root ball and fill around the sides with new soil