Potting Soil Calculator
Estimate potting mix for round containers using pot dimensions, quantity and bag size
Soil to buy
How we calculated it
About the Potting Soil Calculator
Potting Soil Calculator estimates how much growing medium is needed to fill pots, planters, raised containers or several identical containers. Container shape and internal dimensions determine the volume more accurately than guessing from nominal pot size.
Potting mix settles after watering and may be sold by litres, cubic feet or bags. A small extra allowance can be useful, but the appropriate amount depends on the product and how firmly it is placed.
How to Use the Potting Soil Calculator
- Choose the container shape.
- Enter internal diameter, width, length and depth as required.
- Enter the number of containers.
- Calculate total volume and convert it to the bag size sold by your supplier.
How the Calculation Works
A cylindrical pot uses V=πr²h. A rectangular planter uses V=length×width×depth.
The volume for one container is multiplied by quantity, then converted into litres, cubic feet or bag equivalents. Tapered pots may require a frustum formula when the calculator supports different top and bottom diameters.
Worked example
Potting Soil Calculator Worked Example
Four cylindrical pots, 12 in diameter and 10 in deep
Radius=6 in. One pot volume=π×6²×10≈1,131 in³. Four pots total about 4,524 in³, or roughly 2.62 ft³ before settling allowance.
Result guide
Understanding Your Potting Soil Calculator Result
The result estimates internal fill volume. Large root balls, drainage layers or existing soil reduce the amount of new potting mix required.
Before you rely on the answer
Assumptions and Limitations
- Internal container dimensions are used.
- The selected shape approximates the container.
- Displacement from plants, roots or drainage material is excluded unless accounted for.
Practical tip
Using This Result in Practice
For tapered nursery pots, measure both top and bottom diameter if precision matters. Treating every tapered pot as a full cylinder can noticeably overestimate soil.
Related calculations
Useful Calculations to Continue With
If the project is a garden bed or bulk soil area rather than containers, use the Soil Volume Calculator.
If you also need to determine how many plants fit in a bed, use the Plant Spacing Calculator.
Common questions
Potting Soil Calculator FAQ
Should I use inside or outside pot dimensions?
Use inside dimensions for soil volume.
Why can a tapered pot need less soil than a cylinder?
Its lower cross-section is smaller, so the true internal volume is less than a full cylinder with the top diameter.
Should I add extra potting mix?
A modest allowance can help account for settling and spillage, but the amount depends on the mix and project.