How to Use the Potting Soil Calculator
Buying the right amount of potting mix avoids multiple trips to the garden center. Enter your pot's shape and dimensions and this tool calculates how many liters you need, then converts to standard bag sizes. A 90% fill factor is applied — always leave 1 inch at the top so water doesn't overflow when you irrigate.
Common Pot Size Reference
| Pot Diameter | Height | Soil Needed |
|---|---|---|
| 4" (10cm) | 4" | ~0.7L |
| 6" (15cm) | 5" | ~2.1L |
| 8" (20cm) | 7" | ~5.0L |
| 12" (30cm) | 10" | ~16L |
Frequently Asked Questions
What about the drainage layer at the bottom?
A gravel or clay bead drainage layer occupies 10–15% of the pot height. Measure your pot height, subtract the drainage layer, then use the remainder as the soil depth to get an accurate calculation.
How long can I store unused potting mix?
Sealed, unused potting mix lasts 1–2 years if stored in a cool, dry place out of direct sunlight. Once opened, reseal tightly and use within a season to prevent mold and nutrient degradation.