Fish Tank Heater Calculator
Calculate the heater wattage needed for your aquarium based on tank volume and temperature difference.
Heater Wattage Needed
Aquarium heater sizing depends on the tank volume and the temperature difference between room and desired water temperature.
General rule:
- 5 watts per gallon (1.3 watts per liter) for a 10°F (5°C) temperature rise
- 10 watts per gallon (2.6 watts per liter) for a 20°F (10°C) temperature rise
Common tropical fish temperatures:
- Most tropical freshwater fish: 75–80°F (24–27°C)
- Betta fish: 76–82°F (24–28°C)
- Discus: 82–86°F (28–30°C)
Heater placement tips:
- Place near the water flow (filter outlet) for even distribution
- For tanks over 40 gallons (150 L), consider two smaller heaters for redundancy
- Always use a heater with a built-in thermostat
Safety margin: Add about 25% extra wattage for cold rooms or drafty areas.