Calculators / Heater size
Aquarium Heater Size Calculator
Enter your tank size, the temperature your fish need and the temperature of the room.
Heater size chart
Wattage for the standard tank sizes at three room temperatures, for a 78°F tank.
Heater questions
How many watts per gallon does an aquarium heater need?
The common guideline is 3 to 5 watts per gallon to hold the water about 10°F above room temperature. Small tanks lose heat faster for their size, so they sit at the high end; large tanks sit at the low end.
Is it bad to use a heater that is too big?
A modestly oversized heater simply switches on less often. A heater far too powerful for the tank is a risk if its thermostat sticks on, because it can overheat a small tank quickly. Stay close to the recommended size.
When should I use two heaters?
On tanks of about 55 gallons and up, two smaller heaters at opposite ends heat more evenly, and one keeps the tank safe if the other fails.