What Size Heater Do I Need for a 100-Litre Fish Tank?
Calculate the recommended heater wattage for a 100-litre aquarium targeting 26°C in a 20°C room.
How to use this tool
- Enter the water volume of your tank in litres.
- Enter the target water temperature for your fish species.
- Enter the coldest typical room temperature where the tank sits.
- Buy a heater rated at or above the recommended wattage.
Choosing the right heater wattage prevents temperature swings that stress fish — find the ideal size for your 100-litre tank.
Frequently asked questions
- What wattage heater do I need for a 100-litre tank?
- If your room is 20 °C and you want 26 °C (a 6 °C rise), you need about 72 W. A 100 W heater gives a comfortable safety margin.
- Should I use one large heater or two smaller ones?
- Two heaters of half the required wattage is safer: if one fails stuck-on, the second alone cannot overheat the tank. This is especially recommended for tanks over 200 litres.