Aquarium Heater Wattage Calculator
Get a starting heater size from your tank volume. This is a rule of thumb, so treat the answer as a starting point and check the water temperature with a thermometer.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
A common rule of thumb is about 5 watts for each US gallon of water, which is about 1.3 watts per litre. Multiply the tank volume by that rate.
A cool room, a large open top and drafts all push the need higher. A lid helps keep heat in.
Worked example
A tank that holds 20 gal at about 5 watts per gallon suggests a heater near 100 watts.
Questions
Is a bigger heater always better?
No. A heater that is too strong can push the water past the temperature you want, so use a thermostat and check the reading.
Does room temperature matter?
Yes. A cool room makes the heater work harder, so the rule of thumb may need a higher number.
Why check with a thermometer?
The rule is an estimate. A thermometer shows what the water temperature really is.
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