Calculator
Aquarium heater size calculator
Heater power depends on the amount of water and how much warmer it must be than the room. With a 5 °C difference about 1 W per litre (about 4 W per US gallon) is enough.
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How to size an aquarium heater
power [W] ≈ litres × (water temperature − room temperature) × 0.2
Round up to the next common size. A heater that is too strong does no harm while its thermostat works; one that is too weak won't hold the temperature on a cold night. Temperature ranges for fish are in the guide what temperature should an aquarium be.
Heater size calculator
Typical heater sizes
| Water | Room 20 °C → 25 °C | Room 17 °C → 25 °C |
|---|---|---|
| 30 l (8 gal) | 50 W | 50 W |
| 60 l (16 gal) | 75 W | 100 W |
| 110 l (29 gal) | 150 W | 200 W |
| 200 l (53 gal) | 200 W | 2 × 200 W |
| 300 l (79 gal) | 2 × 150 W | 2 × 250 W |
One heater or two
From about 200 l, two smaller heaters are better than one big one. Heat spreads more evenly, and if one fails the other neither overheats the water nor lets it drop sharply.
When a heater fails
A broken heater can stop heating or stick on. Aquarium Monitor measures the temperature continuously and sends a temperature alarm to your phone: when it leaves your range, when it changes too fast, and earlier when the trend shows it is about to cross a limit.
Frequently asked questions
What size heater for a 30 gallon (112 l) tank?
In a heated room (20 °C / 68 °F) with water at 25 °C (77 °F), 100–150 W is enough. In a cold room choose 200 W.
Can an aquarium heater be too powerful?
A working thermostatic heater switches off at the set temperature. The risk is a stuck thermostat: a stronger heater overheats the water faster, which is why an alarm is worth having.
Keep an eye on your tank from your phone
The app is free and ad-free. The monitor runs on your Raspberry Pi.