Potting Soil Volume
Take the cylinder volume and use 85% of it: you need 2–3 cm of watering space below the rim, plus room for drainage material. Potting compost weighs about 0.6 kg a litre.
Your numbers
Soil needed
9.18L
Volume
9,179cm³
Weight (kg)
5.51kg
Formula
Soil needed = π × (Pot diameter ÷ 2) ² × Pot depth × 0.85 ÷ 1000
Compost is sold by litre and settles about 20% once watered, so expect to top it up after a month or two.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Pot diameter (cm)The diameter across the pot’s rim, which is what pot sizes refer to. | 25 | 0 and up |
| Pot depth (cm)The internal depth, a little less than the outside height. | 22 | 0 and up |
Step by step
Quick reference table
Results when only Pot diameter (cm) changes and everything else stays put.
| Pot diameter (cm) | Soil needed (L) | Volume (cm³) | Weight (kg) (kg) |
|---|---|---|---|
| 12.5 | 2.29 | 2,295 | 1.38 |
| 18.8 | 5.19 | 5,191 | 3.11 |
| 25 | 9.18 | 9,179 | 5.51 |
| 37.5 | 20.65 | 20,654 | 12.39 |
| 50 | 36.72 | 36,717 | 22.03 |
What each result means
| Result | At default values |
|---|---|
| Soil needed (L)How much compost the pot takes. | 9.18 |
| Volume (cm³)The space a solid holds — length cubed. | 9,179 |
| Weight (kg) (kg)Mass in kilograms. | 5.51 |
Common mistakes
Compost is sold by litre and settles about 20% once watered, so expect to top it up after a month or two.
Glossary
- Pot diameter
- The diameter across the pot’s rim, which is what pot sizes refer to.
- Pot depth
- The internal depth, a little less than the outside height.
- Soil needed
- How much compost the pot takes.
- Volume
- The space a solid holds — length cubed.
- Weight (kg)
- Mass in kilograms.
Frequently asked questions
Q. How is Potting Soil Volume calculated?
Soil needed = π × (Pot diameter ÷ 2) ² × Pot depth × 0.85 ÷ 1000 — Take the cylinder volume and use 85% of it: you need 2–3 cm of watering space below the rim, plus room for drainage material. Potting compost weighs about 0.6 kg a litre.
Q. Can you walk through an example?
With Pot diameter 25cm, Pot depth 22cm, the answer is Soil needed 9.18L.
Q. What do I need to enter?
Enter Pot diameter, Pot depth. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Pot diameter (cm) moves the answer to Pot diameter (cm) 12.5 → Soil needed (L) 2.29 and Pot diameter (cm) 50 → Soil needed (L) 36.72. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Compost is sold by litre and settles about 20% once watered, so expect to top it up after a month or two.
Related calculators
Keep your length units consistent across inputs — mixing centimetres and metres throws results far off.