What size hot water cylinder do I need?
Sizing by household, and why going one size up is usually cheaper than regretting it.
Last reviewed 2026-09-02
Cylinder sizing is done by how many people run hot water in the same part of the day, not by the size of the house.
| Household | Typical size |
|---|---|
| 1–2 people | 135–180 litres |
| 3–4 people | 200–250 litres |
| 5+ people | 300 litres and up |
The quickest check
Look at the cylinder you have now. There is a data plate on the side with the capacity stamped on it. If nobody in the house has ever complained about running out, the same size again is the safe answer.
When to go up a size
If the last person to shower in the evening gets a cold one, go up. The price difference between 200L and 250L is small compared to living with it for the next fifteen years.
When not to
A bigger cylinder holds more water hot around the clock, so it costs a little more to run. There is no point buying 330 litres for two people.