Aquarium Heater Calculator
Find the right heater wattage for your tank size and room temperature.
How it works
A rule of thumb is 1 watt per litre for a small temperature rise. For larger rises (cold rooms) use 1.5 watts per litre. Required watts ≈ Volume (L) × factor, rounded up to the nearest available heater, and split across two heaters in large tanks.
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Formula & Method
A rule of thumb is 1 watt per litre for a small temperature rise. For larger rises (cold rooms) use 1.5 watts per litre. Required watts ≈ Volume (L) × factor, rounded up to the nearest available heater, and split across two heaters in large tanks.
Example Calculation
A 100 L tank in a moderately heated room needs roughly a 100 W heater; in a cold room, a 150 W (or two 75 W) heater is safer.
Frequently Asked Questions
What size heater do I need for my tank?
About 1 watt per litre when the room stays within 5 C of your target temperature, rising to 1.5 watts per litre for cold or uninsulated rooms. A 200-litre tank in a normal Australian living room needs roughly 200 W; the same tank in an unheated garage needs closer to 300 W.
Should I use two heaters instead of one?
On tanks over about 200 litres, yes. Two half-sized heaters mean a single failure cannot leave the tank cold or overheat it rapidly. Place them at opposite ends in areas of good water movement.
What temperature should a tropical aquarium be?
Most tropical community fish do well between 24 and 26 C. Check the species profiles for your specific fish, since discus want 28-30 C while white cloud minnows prefer 18-22 C.
Do I need a heater in Australia?
For tropical species, yes, in almost all of the country. Native Australian fish, white cloud minnows and goldfish generally do not need one. Even in Brisbane, winter night temperatures drop enough to stress tropical fish without heating.
Why is my heater running constantly?
Either it is undersized for the room temperature, the tank is losing heat through an open top, or the thermostat has failed. Check with an independent thermometer before replacing anything.