Pot Volume Is Geometry

A round pot is a cylinder: π × radius² × depth, converted from cubic inches to cubic feet (÷ 1,728). A square pot is side² × depth. A 10-inch round pot, 8 inches deep, holds 0.36 cu ft — about 9.3 quarts. The calculator does the unit conversions so you can compare any pot to any bag label.

Bags Are Sold in Two Languages

Retail potting mix comes in 1.5–2 cu ft bags, often also labeled in quarts (1.5 cu ft ≈ 40 qt). Buying one bag for five 10-inch pots fails; buying two bags for one 12-inch pot leaves you storing soil. The calculator converts to both units and rounds up to whole bags, so the trip to the garden center happens once.

Fill Is a Feature, Not Waste

The 90% default isn't under-filling — it's the headroom that keeps water in the pot instead of over the rim and prevents soil washing out during watering. Fill level is adjustable: seeds start lower, established transplants can go near-full, and the total adjusts automatically.