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Category: Calculators
Electricity Cost Calculator
Turn watts and hours into a cost per day, month and year.
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About this tool
Works out what an appliance costs to run - per hour, per day, per month and per year - from its power in watts, how long it runs, and the price you pay per kilowatt-hour.
A bill is not one price, which is why there are two rate fields here rather than one. Electricity is sold as energy, and it is delivered by a distribution network that charges separately, also per kilowatt-hour. Both appear on the bill, both scale with what you use, and a calculation that uses only the energy rate understates the real cost by roughly the same amount again. Take both numbers from your own invoice rather than from a tariff page: the fixed monthly charges are not per-kWh and should be left out.
Standby is the field people skip and should not. A device drawing 1 W around the clock uses 8.8 kWh a year, which is little on its own and considerable across a household of televisions, consoles, chargers, set-top boxes and always-on speakers. A 100 W appliance used four hours a day and a 5 W standby for the other twenty hours are closer in annual cost than anyone expects.
Watts are on the rating plate, usually on the back or underneath. Where a device shows amps instead, multiply by the voltage - 230 V in Poland and most of Europe - to get watts. Anything with a heating element or a motor is the expensive category: kettles, ovens, dryers, irons and heaters draw one to three kilowatts, while electronics rarely reach a tenth of that. A 2 kW heater for three hours costs more than a laptop running all month.
The arithmetic is deliberately simple and transparent: watts, hours and price, multiplied out. Nothing is stored and nothing is sent anywhere.
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Good to know
Questions people actually ask
- Why are there two prices per kWh?
- Because a bill has two variable parts. The energy itself is one rate, and the distribution network charges another, also per kilowatt-hour. Only counting the first understates the true cost by roughly as much again. Take both from your own invoice; the fixed monthly standing charges are not per-kWh and belong outside this calculation.
- Where do I find an appliance's wattage?
- On the rating plate - usually a sticker on the back or underneath, or in the manual. If it is given in amps rather than watts, multiply by the mains voltage (230 V in Poland and most of Europe). A device labelled 2.2 A therefore draws about 500 W.
- Does standby power really matter?
- More than it sounds. One watt drawn continuously is 8.8 kWh a year. That is trivial for a single device and adds up across a household of televisions, consoles, chargers, set-top boxes and speakers that are never truly off. It is worth entering, precisely because it is the part nobody counts.
- Which appliances actually cost the most?
- Anything that makes heat or turns a motor. Kettles, ovens, tumble dryers, irons and electric heaters draw one to three kilowatts; electronics rarely reach a tenth of that. A 2 kW heater running three hours a day costs more than a laptop left on all month - which is why the heating decisions are the ones worth calculating.
- Does this account for a variable or time-of-use tariff?
- No - it applies one rate to all the hours you enter. For a two-rate tariff, run the calculation twice with the day and night hours split, once at each price, and add the results.