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Heater wattage
calculator

How many watts does your tank need? From volume, room and target temperature – as a guideline for your purchase decision.

Tank & location
Volume
Temperatures
Result
Enter volume and temperatures.
Help – setup location & margin

Setup location: A tank with a lid in an evenly warm room loses less heat than an open tank in a drafty hallway or basement.

Lowest room temperature: Not the average, but the coldest realistic value (e.g. a winter night with the heating off) – your heater still needs to keep up then.

Margin: In borderline cases, round up to the next standard size. Two smaller heaters instead of one large one also add redundancy.

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Aquarium volume

Work out net liters from your tank dimensions – the basis for this calculator.

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Water change calculator

Calculate liters – from a percentage or directly from your target nitrate.

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Unit converter

Liters, gallons, °C/°F, GH/KH to ppm – every aquarium unit in one place.

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CO₂ calculator

How long does it take for the tank to reach the CO₂ target after startup?

Frequently asked questions
How many watts of heater do I need for my aquarium?
A rough rule of thumb: wattage ≈ volume in liters × temperature difference (target minus coldest room temperature) × factor 0.1–0.25, depending on the setup location. A 200-liter tank with an 8°C difference in a normal room needs roughly 200 × 8 × 0.15 ≈ 240 watts.
Is an oversized heater bad?
Not inherently – modern heaters with a good thermostat simply switch off sooner. But an oversized heater can heat up dangerously fast if the thermostat fails. When in doubt, use two smaller heaters instead of one very large one.
Where should the heater be placed in the aquarium?
Ideally in the filter outlet's flow, so heat is distributed evenly. Avoid placing it directly on the substrate (heat buildup, burn risk for bottom dwellers) and keep it away from the glass.
Do I still need a heater in a warm room?
Usually yes – even warm rooms often swing more at night or in winter than you'd expect. A heater with a thermostat keeps the target temperature stable regardless of room temperature.