Pot Size Calculator

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:

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