Potting Soil Volume Calculator
Calculate liters and US quarts of mix for round or tapered pots. Enter inside dimensions, subtract root-ball space, and plan multiple pots.
Measure the inside of the pot and the depth you will actually fill. Leave space below the rim for watering.
Choose your inputs and use the button above to get a result.
How the volume is calculated
For a round tapered pot, volume = π × depth × (top diameter² + top diameter × bottom diameter + bottom diameter²) ÷ 12. With centimeter inputs, divide by 1,000 to get liters. Equal top and bottom diameters give a cylinder. Inches are converted to centimeters before the calculation.
The result subtracts the root-ball percentage you choose and multiplies by the number of pots. The percentage is your estimate, not a measurement the tool can infer. For example, if the root ball takes about one third of the usable space, enter roughly 33%. Use 0% for empty pots or a first estimate of full capacity.
Turn volume into a potting mix
Take the result to the soil mix calculator to split a batch into ingredients. Mix settles and bark pieces leave irregular spaces, so buy a little extra rather than treating the output as a bag guarantee. US quarts are liquid quarts; bagged substrates may be sold using other package conventions.
This model assumes a circular cross-section and straight taper. It does not fit square planters, curved bowls, or a pot with a reservoir. Do not add a gravel layer to compensate for missing drainage. See soil and repotting before choosing a new container.
Frequently asked questions
Should I measure outside diameter?
Use inside diameter. Thick walls and a rolled rim can make outside dimensions overstate the usable volume.
Does this tell me the correct next pot size?
No. It estimates mix for a chosen pot. Use the pot size calculator and inspect the roots to decide whether to size up.