Aquarium Heater Wattage Calculator
Estimate heater power from water volume and the temperature rise above your room temperature.
US liquid gallons (1 US gal = 3.785411784 L). Switching units converts your entries.
Check the entered values and ranges before calculating.
Result
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Reference table
| Volume | 5 °C diff | 10 °C diff | 15 °C diff |
|---|---|---|---|
| 50 L | 25W | 50W | 75W |
| 100 L | 50W | 100W | 150W |
| 200 L | 100W | 200W | 300W |
| 400 L | 200W | 400W | 600W |
Use the temperature rise to estimate heater power
Enter the aquarium’s working water volume, the lowest expected room temperature and your chosen water temperature. The result applies a simple watts-per-liter rule after converting US units when selected.
Formula and units
Temperature rise = target − room temperature. Use 0.5 W/L up to 5°C (9°F), 1 W/L up to 10°C (18°F), or 1.5 W/L above that; round the total up to a whole watt.
Worked example
For 50 US gallons (189.27 L), a 68°F room and a 77°F target, the rise is 9°F (5°C). The estimate is 95 W, before checking available heater sizes and the manufacturer’s sizing chart.
Assumptions and limits
Surface area, evaporation, insulation, room airflow and a sump affect heat loss. This rule does not model them. Splitting total power across two heaters does not guarantee that either one alone can maintain temperature if the other fails.
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Frequently Asked Questions
How is heater wattage estimated?
The calculator applies 0.5 W/L for a temperature rise up to 5°C (9°F), 1 W/L up to 10°C (18°F), and 1.5 W/L above that. This is a simple sizing rule, not a model of heat loss.
Will two smaller heaters provide full backup?
Not necessarily. Two heaters split the estimated total power; if one fails, the remaining heater may not maintain the target temperature. Check manufacturer ratings, room conditions and controller arrangements when planning redundancy.
Which room temperature should I use?
Use the lowest realistic room temperature near the aquarium, not just a daytime average. An open top, drafts and evaporation can increase heat loss. Verify actual water temperature after installation and follow the heater’s placement instructions.
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