Aquarium Heater Size Calculator
The aquarium heater size calculator recommends the heater wattage your tank needs. Enter your water volume and, optionally, your room and target temperatures to get a suggested wattage. Sizing your heater correctly keeps temperature stable, which is one of the most important things you can do for fish and coral health.
As a rule of thumb you’ll want roughly 3 to 5 watts per gallon, and more when your room runs cold or your target temperature is well above ambient. For most reef and tropical tanks a target of 76 to 78 degrees Fahrenheit is ideal.
Formula: Watts ≈ gallons × 3 to 5 (use more for a larger room-to-tank temperature gap)
Frequently Asked Questions
What size heater do I need for my aquarium?
Plan on roughly 3 to 5 watts per gallon, using more when the gap between room temperature and your target is large. A 40 gallon tank in a normal room needs about 150 to 200 watts. Enter your volume and temperatures above for a tailored recommendation.
Should I use one heater or two?
For tanks above about 40 to 50 gallons, two smaller heaters that together meet the wattage are safer than one large heater. If a heater sticks on, a single undersized unit cannot cook the whole tank, and if one fails off the other keeps things stable.
Where should I place an aquarium heater?
Put the heater in an area of strong flow, such as near a return or powerhead, so heat distributes evenly. A sump is ideal. Use a separate thermometer or controller to verify temperature, since built-in heater dials are often inaccurate.
