Aquarium Electricity Cost Calculator
Enter the wattage of each device and your electricity price. Unlike most calculators, this one applies a duty cycle to the heater — a thermostat-controlled heater is only actually drawing power for a fraction of the day — so the result reflects what your meter will really show, not a worst-case number three times too high.
Calculate running cost
kWh = watts × hours ÷ 1000. Enter the price from your utility bill; the result is in the same currency.
Why most estimates are two to three times too high
Search for “aquarium electricity cost” and most tools multiply your heater’s rated wattage by 24 hours. That is not how thermostats work. A correctly sized heater switches on, raises the water a fraction of a degree, and switches off; in a normally heated home it typically draws power only 20–50% of the time. A 100 W heater at a 35% duty cycle uses about 25 kWh a month — not the 73 kWh a naive calculation gives. Everything else in the calculation really is simple arithmetic:
heater hours per day = 24 × duty cycle
What drives the duty cycle
The heater only replaces heat the tank loses, and heat loss is driven by the gap between room and water temperature, the tank’s surface area, and evaporation. Practical consequences:
- Room temperature dominates. A tropical tank at 25 °C in a 22 °C living room barely works its heater; the same tank in a 15 °C basement can run 60–70% duty in winter. Expect a visible seasonal swing on your bill.
- A lid is the cheapest insulation. Evaporation is the largest single heat-loss path from an open-top tank; a glass lid can cut heating energy substantially, and polystyrene under the tank and foil-faced foam on the back panel help further.
- Bigger tanks are more efficient per litre. Volume grows faster than surface area, so a 200 L tank does not cost twice as much to heat as a 100 L.
- Heater size does not change consumption. A 200 W heater in a tank that loses 20 W of heat simply runs a 10% duty cycle. Energy used equals heat lost, whatever the label says — so “downsizing the heater to save power” does not work.
Measuring instead of estimating
A plug-in energy meter (sold as Kill A Watt and many other names, typically 10–25 in local currency) sits between the plug and the wall and logs cumulative kWh. Run your heater through it for a week in each season and you will have a duty-cycle figure better than any calculator’s assumption. Metering is also the quickest way to catch a failing thermostat — a heater stuck near 100% duty in a warm room is a warning sign worth investigating before it cooks the tank.
Frequently asked questions
How much does a typical tank cost to run?
Order of magnitude, at 0.17 per kWh: a 60 L tropical tank with a 50 W heater, small LED light and internal filter lands around 3–5 per month. A 300 L tank with a 250 W heater, bigger light and external filter is more like 12–20. High-tech planted tanks and marine systems (strong lighting, pumps, chillers) can be several times that.
Does a bigger heater use more electricity?
No. Consumption equals the tank’s heat loss, which the heater size does not change — a larger heater just reaches set temperature in shorter bursts. Sizing should follow recovery speed and reliability (see our heater size calculator), not the power bill.
Is it cheaper to lower the tank temperature?
Each degree of temperature difference to the room adds roughly proportionally to heat loss, so yes — running at 24 °C instead of 27 °C in a 20 °C room cuts heating energy by roughly a third. But set temperature by the needs of your species first; the saving is real but small next to animal welfare. Check reputable care guides for your fish before changing anything.
Are LED lights worth the upgrade?
Usually, on running cost alone: an LED fixture delivers similar usable light to an old T8/T5 setup at roughly half the wattage or less, runs cooler, and lasts years longer. On an 8–10 hour photoperiod the saving compounds; use the calculator above with your actual wattages to see the payback period.