How the calculation works
Each row is the same small formula:
kWh/day = watts × hours ÷ 1000 month = day × 30.44 · year = day × 365.25 · cost = kWh × price per kWh For the heater, “hours” is not the hours it is switched on; it is the hours it actually runs, which the heater calculator estimates with a thermostat duty-cycle model. That is why a 200 W heater does not cost twice a 100 W one: it runs half as long to replace the same standing heat loss. Filters and air pumps run the full 24 hours, lights run their photoperiod, and the totals card adds every row into daily, monthly and annual figures, with the heater's share called out so you know where the money goes.
Working device by device
Add as many rows as you need with the chips (a second heater, UV steriliser, auto-doser, anything). Rename rows to match your gear, enter rated watts and realistic daily hours, and each row shows its own kWh and cost immediately. Delete what you don't have; the defaults only exist so the tool is useful before you touch it. Everything recalculates as you type. Nothing is submitted or stored, and the tool is free for everyone with no account.
Where the savings actually are
Totals make the levers obvious. If heating dominates the bill, a lid, insulation under and behind the tank, or a room that stays warmer will save more than any equipment swap. Heat loss to the room is the cost. If lighting dominates, trim the photoperiod or move to LED. Filters are cheap to run but choose the flow your tank needs rather than the biggest label. The one thing that never helps: swapping a heater for a smaller one that then runs flat out; it costs the same and heats slower.
Frequently asked questions
How much electricity does an aquarium use per month?
A typical 100 litre community tank with a filter (8 W, 24 h), light (30 W, 8 h), air pump (4 W, 24 h) and a 100 W heater cycling at a small duty runs roughly 25–40 kWh per month at $0.30/kWh, about $8–12. A big cichlid tank with strong lighting can use several times that; a small unheated bowl far less. The calculator above replaces these typical numbers with your own gear.
What uses the most power in an aquarium?
It depends on the tank, and the calculator makes that visible per device. In warm homes the filter and lights often dominate; in cold rooms the heater can dwarf everything else; on planted tanks high-output lighting leads. The heater’s share is shown in the totals card. A lid, insulation or a warmer room usually saves more energy than any equipment swap.
How do I find each device’s wattage and my electricity price?
Wattage is printed on the device label, power brick or pump body. Use the rated watts, not the flow or lumen figures. Your electricity price is the per-kWh energy rate on the utility bill (excluding fixed daily fees), roughly $0.10–0.45 per kWh in most countries. A cheap plug-in power meter measures the real draw if the label is unreadable.
Do heaters and filters use more power than the label says?
Heaters are the special case: the label is the maximum draw, but a thermostat means they only run a fraction of the day, which is exactly what the duty-cycle model accounts for. Filters, air pumps and wave makers draw close to their rated watts whenever they run. Lights sit in between: LED fixtures draw their rated power but only during the photoperiod you enter.
How can I lower my aquarium’s electricity bill?
The biggest wins are heat-related: a snug lid, insulation under and behind the tank, and keeping the heater away from drafts. Then trim the photoperiod to what your plants and fish actually need, and choose modern LED lighting and an appropriately sized filter. Bigger heaters do not help or hurt the bill; they just cycle less often.
Does the calculator include the cost of the aquarium itself?
No. This tool covers running costs only: the electricity your equipment consumes. Set-up costs (tank, stand, gear) and consumables (food, water conditioner, filter media) are separate. The per-year figures here are what shows up on your energy bill because of the tank.
Related calculators
The heater is usually the interesting row: size it with the heater calculator, weigh alternatives on the heater size comparison, and measure the water those devices keep warm with the aquarium volume calculator.