Free heater wattage calculator. Enter tank volume + room temperature + target tank temperature, get the recommended heater wattage. Avoid undersized heaters that cycle constantly + oversized ones that overshoot target.
Aquarium heater wattage scales with tank volume and the temperature differential you need to maintain. The widely-cited "3-5 watts per gallon" rule is approximate - rooms cooler than 65°F or tanks deeper than 18 inches need more, while warm rooms need less.
Key tip: two smaller heaters usually beat one larger one. Two 100W heaters in a 50-gallon tank give you redundancy if one fails (no surprise tank-killing temperature crash) and finer thermostat control. Always pair heaters with a controller (Inkbird, Apex, Hydros) that overrides the heater's built-in stat.
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