Finding the Right Aquarium Heater Size
The basic rule of thumb for wattage is to use between 2.5 and 5 watts per gallon of actual water volume in the aquarium. You can use a single unit of the correct size or multiple units that add up to the needed wattage. But then you need to adjust for the temperature of the room and the temperature desired in the tank.
First, subtract the average temperature of the room the aquarium is located in from the temperature at which you wish to maintain the aquarium water.
Using the Aquarium Heater Size Guide below, find the size of your aquarium in the left-hand column and move to the column that shows the number of degrees the aquarium needs to be heated. If the heating requirement is between levels, move up to the next larger size.
In larger tanks, or a situation where the room temperature is significantly below the desired water temperature, two heaters may be required.
Heaters should be installed at opposite ends of the aquarium to heat it more evenly.
Average Room Temp = 68 degrees F
Desired Water Temp = 77 degrees F
Heating required = 9 degrees F
Tank Size = 20 gallon
Heater size needed = 50 watts
Aquarium Heater Size Guide
5 Degrees C, 9 Degrees F
10 Degrees C, 18 Degrees F
15 Degrees C, 27 Degrees F
|5 Gallon/25 Liter||25 watt||50 watt||75 watt|
|10 Gallon/50 Liter||50 watt||75 watt||75 watt|
|20 Gallon/75 Liter||50 watt||75 watt||150 watt|
|25 Gallon/100 Liter||75 watt||100 watt||200 watt|
|40 Gallon/150 Liter||100 watt||150 watt||300 watt|
|50 Gallon/200 Liter||150 watt||200 watt||two 200 watt|
|65 Gallon/250 Liter||200 watt||250 watt||two 250 watt|
|75 Gallon/300 Liter||250 watt||300 watt||two 300 watt|