Enter your aquariums volume in gallons. Enter your gallons in the correct area, if you have an acrylic or glass aquarium.

The answers provided are estimates of what you will require in terms of wattage. 

It is recommended that you divide the number given in half, round each number up to the closest available heater size and use two of those sized heaters instead of one.
This will give you a good safety factor, in case one heater fails, the other will be able to still heat the tank until you replace the broken one.