What Size Aquarium Heater Do I Need for My Fish Tank?

What Size Aquarium Heater Do I Need for My Fish Tank?

Does My Aquarium Need a Heater?

Temperature and heater requirements depend on the type of fish you plan to keep. Notably, most tropical aquarium fish and plants thrive in a temperature range of 22 - 26°C. However, if you’re keeping coldwater fish, their preference is a temperature range of 15 - 20°C. 

Even if your climate is in the warmer range, an aquarium heater is still a good idea. Heaters come equipped with a thermometer, which will monitor the water temperature in your aquarium, allowing them to switch on and off to regulate your temperature. 

It’s also important to run a second, independent thermometer that is separate to your heater, so that you can manually monitor temperature in case of problems with your heater. 

Appropriate temperatures are critical for fish, who cannot produce their own body heat, and rely on the temperature of the water to maintain a healthy body temperature. 

The best placement for your aquarium heater is near the water flow, such as the outlet of the aquarium filter. This helps the heater warm your tank faster, evenly and quickly distributes warm water throughout your aquarium. 

How Do Aquarium Heaters Work?

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 Aquarium heaters convert electrical energy into heat. Over time, the heater increases and maintains the temperature of your aquarium. 

Watts are a measure of how much energy an aquarium heater generates. The higher the wattage of a fish tank heater, the higher the temperature increase that can be produced. 

What Size Heater Do I Need For My Aquarium?

You can easily work out the ideal heater size for your aquarium by first working out the volume of water held in your tank.

How Do I Calculate Water Volume in my Aquarium Tank?

Illustration of stationary icon Free Vector To calculate the water volume of your fish tank, first measure the length (in metres), height (in metres) and width (in metres) of your tank:

Volume (m³) = Length (m) x Height (m) x Width (m)

Multiple by 1,000 to convert m³ to litres. 

Example: If your tank measures Length 1.22m, height 0.46m and width of 0.36m, your calculation will look like this:

1.22m x 0.46m x 0.36m = 0.2m³

Multiply 0.2m³ by 1000 = 200 litres.

What Fisk Tank Temperature Increase Do My Fish Need?

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 Next you will need to work out the maximum temperature increase required to heat your aquarium water to the optimal temperature for your fish. 

Example:Assuming you live in Melbourne, with an aquarium inside, your temperature might dip to 15 °C in winter. For tropical fish, this is at least 10 °C cooler than they require for optimal health. Therefore, work out your temperature increase:

25°C  - 15°C = 10°C 

How To Calculate the Right Size Aquarium Heater (in Watts):

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Lastly use the Aquarium Size and Required Aquarium Temperature Increase in the table below to calculate the required aquarium heater wattage:

Aquarium Size

Required Aquarium Temperature Increase




50 Litres

50 Watt

75 Watt

75 Watt

100 Litres

75 Watt

100 Watt

200 Watt

150 Litres

100 Watt

150 Watt

300 Watt

200 Litres

150 Watt

200 Watt

2 x 200 Watt

250 Litres

200 Watt

250 Watt

2 x 250 Watt

300 Litres

250 Watt

300 Watt

2 x 300 Watt

Example: If your aquarium is 200 litres and you need to increase the temperature by 10 °C, then your aquarium requires a 200 Watt heater.

If the exact size heater you require isn’t available, it’s always better to install a heater that is ‘too large’ rather than one which is too small. A heater which is too large will quickly and efficiently heat your aquarium water, switching off once the ideal temperature is reached. However, a heater that is too small, will take much longer to reach the desired temperature and it many cases may not reach it at all. A heater that is too small is therefore inefficient and often unviable. It will also, in the long run, cost you more to run. 

In case of heater failure, it’s ideal to have a second, back-up heater ready to install. Therefore if your existing heater fails, you can immediately install your back-up heater and avoid the risk of endangering your fish or plants. 

With the above guide, you’re well on your way to equipping your fish with the ideal temperature and environment needed to help them thrive!

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