🌡️ Aquarium Heater Wattage Calculator
Find the right heater size based on your tank volume and temperature requirements.
Results
Recommended Heater
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Minimum wattage
Watts per Gallon
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Calculated
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Dual Heater Setup
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For tanks >75 gallons, two smaller heaters provide redundancy
Watts = Gallons × Watts-per-Gallon
W/gal: ΔT ≤ 5°F → 3, ΔT ≤ 10°F → 4, ΔT > 10°F → 5
Round up to nearest standard heater size (50, 100, 150, 200, 250, 300W…)
W/gal: ΔT ≤ 5°F → 3, ΔT ≤ 10°F → 4, ΔT > 10°F → 5
Round up to nearest standard heater size (50, 100, 150, 200, 250, 300W…)
Choosing the Right Aquarium Heater
The general rule of thumb is 3-5 watts per gallon, but the actual requirement depends on the temperature differential between your room and target water temperature.
Watts Per Gallon Guide
| Temp Difference | Watts/Gallon | Example (75 gal) |
|---|---|---|
| ≤ 5°F | 3 W/gal | 225W |
| 5-10°F | 4 W/gal | 300W |
| > 10°F | 5 W/gal | 375W |
Why Use Two Heaters?
For tanks over 75 gallons, using two smaller heaters is recommended. If one heater fails stuck-on, a single smaller heater won't overheat the tank as quickly, giving you time to catch the problem. It also provides backup heating if one heater fails off.