How to use this aquarium electricity cost calculator
Enter the electricity price in whole currency units per kilowatt-hour: for twenty cents, use 0.20, not 20. Choose a currency label and a whole-day period from 1 to 366. Edit the sample devices or add your own, up to twenty rows. Enter operating watts, scheduled hours per day, and the percentage of those hours during which that power is drawn. Remove equipment that is not part of your setup.
How the calculation works
Watts measure power; kilowatt-hours measure energy over time. A 20 watt device drawing that power for 24 hours uses 480 watt-hours, or 0.48 kWh. Multiply kilowatt-hours by a price per kWh to estimate the variable energy charge. The calculator sums individual device energy before applying the same entered tariff. It does not obtain local tariffs, taxes, or exchange rates automatically.
Scheduled time and duty cycle describe different things. A heater may be available all day but actively heating for only part of that time. Entering 24 scheduled hours with a 25% active duty models six equivalent full-power hours. The default duty is only an example. Actual heater demand varies with conditions; the calculation does not predict room temperature, heat loss, thermostat behavior, or seasonal heating requirements.
Avoid applying the duty factor twice. If you already measured that a device draws full operating power for six hours per day, enter six hours with 100% duty, not six hours with 25%. Likewise, when using measured average watts across the scheduled period, use 100% duty because cycling is already included in that average. Mixing these conventions can make the resulting cost much too low.
The chosen period multiplies a constant daily schedule by the number of days entered. The annual estimate independently uses 365 days, rather than twelve copies of a 30-day month. These are projections, not meter readings. Variable light programs, dimming, temperature changes, intermittent equipment, and standby consumption need separate treatment or measurements that capture their actual average energy use.
Electricity bills may include fixed standing charges, tiered prices, time-of-use rates, taxes, discounts, and minimum charges. This tool models a single variable energy rate only. A cost comparison should use the relevant marginal rate, not necessarily the entire bill divided by energy use. Selecting USD, CAD, GBP, or AUD changes display labels but never converts the entered price or applies regional billing rules.
Formulas
Device energy per day
Period cost
Annual projection
Worked examples
Filter, light, and cycling heater
A 20 W filter at 24 hours uses 0.48 kWh/day. A 30 W light at eight hours uses 0.24 kWh/day. A 150 W heater available 24 hours at an illustrative 25% duty uses 0.9 kWh/day. Total daily energy is 1.62 kWh.
Applying a tariff
At 0.20 currency units per kWh, 1.62 kWh/day costs 0.324 per day, 9.72 for 30 days, and 118.26 for 365 days. A 31-day period costs 10.044 before display rounding. These amounts exclude fixed charges and assume the same daily equipment use throughout.
Common uses
Compare equipment running costs
Hold runtime and tariff assumptions constant when comparing two devices. Lower rated watts do not necessarily mean equivalent aquarium performance, so cost should remain separate from suitability and life-support requirements.
Explore seasonal heater scenarios
Compare different justified duty estimates instead of pretending that one example predicts every season. Meter readings over representative periods can help check whether an assumed average is plausible for the real installation.
Accuracy and limitations
The model assumes constant operating power while active, zero consumption during modeled inactive time, and repeated daily use. Include standby separately when material. Blank or out-of-range entries return validation messages instead of silently using zero.
Displayed currency values round to two decimal places, while energy and totals use unrounded calculations. The annual result uses 365 days and excludes fixed charges, tariff tiers and seasonal changes. It is not a guaranteed bill.
Sources and methodology
References support unit conversions, relevant material or energy calculations, and husbandry context where listed. NumUtility's geometric and arithmetic models are explained above; they do not establish safe stocking, maintenance requirements, or structural capacity.
Frequently asked questions
Does the heater run at its rated power all day?
Not necessarily. A thermostat cycles it. Enter a measured or justified duty estimate; the sample 25% value is not a forecast for your aquarium.
Can I use a plug-in energy meter?
Yes. A representative meter reading can help establish average power or validate the projected kWh. Follow device and electrical-safety instructions, especially near water.
Can this calculate my exact electricity bill?
No. It estimates listed equipment's variable energy charge under one tariff and repeated schedules. It excludes other household loads and fixed or complex billing components.
Are my aquarium measurements saved?
No. These calculations run locally in your browser. Entered measurements are not sent to NumUtility, and no account or saved aquarium profile is required.