Pot Size Calculator
Measure across the root ball of your plant and choose how fast it grows. The calculator suggests the next pot size, its volume, how much compost you need and the drainage it likes.
- From the root ball
- Slow to fast growers
- Volume and compost
Measure the root ball at its widest, or the inside top width of the pot it is in now.
The best new pot is only a little bigger than the old one. Most plants do well in a pot about 5 cm wider than the root ball. A pot much bigger holds wet compost the roots cannot reach, which can rot them.
Pot size chart
Most plants. Search for a size.
| Root ball (cm) | Pot (cm) | Pot (in) | Volume (L) |
|---|---|---|---|
| 5 | 12 | 4.7 | 1 |
| 10 | 15 | 5.9 | 2 |
| 15 | 21 | 8.3 | 5.5 |
| 20 | 27 | 10.6 | 11.6 |
| 25 | 30 | 11.8 | 15.9 |
| 30 | 35 | 13.8 | 25.3 |
| 40 | 45 | 17.7 | 53.7 |
| 50 | 60 | 23.6 | 127.2 |
Pot size is the width across the top. Volumes are approximate.
Root ball and pot
Most plants. Slide the root ball.
The pot is drawn in section with the root ball sitting in the top of the compost.
How to repot a plant
One size up. Step through it.
Water first
The day before.
Spring is the best time to repot, as the plant is starting to grow.
Plastic, terracotta or glazed
Pot types. Compare them.
Light and cheap.
Clay that breathes.
Sealed ceramic.
Every pot needs a drainage hole. Without one, water collects and the roots rot.
Before repotting
Potting checks. Tick each item.
Tick each item as you go.
Roots circling the bottom or growing out of the drainage holes mean it is time to repot.
What you get
Pot sizing. Each tile explains one result.
cm or inches.
Litres.
US pots.
To buy.
Advice.
Plants in pots that are too large stay wet for days, which is the most common cause of root rot.
Frequently Asked Questions
No question matches that search.
How much bigger should a new pot be?
About 5 cm, or 2 inches, wider than the root ball for most plants.
Can a pot be too big for a plant?
Yes. Extra compost stays wet and can rot the roots.
How do I know when to repot?
Roots circle the bottom, grow out of the holes or the plant dries out very fast.
What size is a one gallon pot?
About 17 to 19 cm across the top, holding just under 4 litres.
How much compost do I need for a pot?
About the pot's volume plus 10%, as compost settles.
Do cacti need small pots?
Yes. They like snug pots and gritty, fast-draining compost.
Should I put gravel in the bottom of a pot?
It is not needed. A drainage hole and good compost drain better.
A pot that fits the roots
Go up one size at a time, about 5 cm wider, with good drainage. The plant settles in quickly and grows into its new pot.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.