Appliance Energy Cost Calculator
Find out what an appliance costs to run: enter the wattage, hours used per day, standby draw and your electricity price to get daily, monthly and yearly cost.
About this tool
An appliance that costs a few pennies an hour does not look expensive next to its purchase price. Run it every day for a year and the picture changes. This calculator turns the number on the rating label into the number that actually matters: what it adds to your bill.
The arithmetic is simple, but two things trip people up. The first is the price. Electricity is billed per kilowatt hour, and that rate varies enormously from one country to the next, so the calculator asks you for it rather than guessing. Your bill states it plainly, and once you have it the answer is in your own currency.
The second is standby. Most appliances keep drawing power when you switch them off — the little light, the remote sensor, the clock. That trickle runs around the clock and is easy to forget, so it is calculated separately here and shown as a share of the total. If the figure surprises you, that is the point.
Standby power: the cost that never switches off
The hours you leave blank are counted as standby. Fill in 4 hours of use and the other 20 are treated as idle, so a 5 watt standby draw becomes 0.1 kWh a day — small per day, but 36.5 kWh over a year.
This is the one part of the calculation most tools leave out, and it is the part that tends to surprise people. Five watts is nothing in isolation. Left plugged in for the 8,760 hours in a year it quietly becomes a real line item, and it is the reason a household can have nothing switched on and still see the meter turn.
The calculator treats the two states as strictly complementary. If you say the appliance runs four hours a day, the remaining twenty are standby. That is why entering 24 hours of use produces zero standby cost no matter what standby figure you typed: there is no idle window left for it to occupy.
If you do not know the standby figure, leave it blank rather than guessing. The result then covers the running cost only, which is an honest answer. Many plug-in energy monitors will read standby draw directly, and the manual sometimes states it as a separate line alongside the rated power.
Kilowatts and kilowatt hours are not the same thing
A kilowatt is a rate and a kilowatt hour is a quantity. A 2,000 watt appliance running for one hour uses 2 kWh; the same appliance running for 15 minutes uses 0.5 kWh, even though its rating never changed.
Confusing the two is the single most common way to get a running cost wrong by a factor of ten or more. The wattage on the label tells you nothing about consumption on its own. Consumption is the wattage multiplied by the time, and only then do you have something you can price.
It helps to read the units aloud. The wattage is "joules per second" — how fast energy is being used. The kilowatt hour is a total. Your meter measures the total, and your bill charges for the total, which is why the two multiplications in the formula map exactly onto the two lines you can see: the label and the bill.
The formula the calculator applies is therefore price multiplied by power multiplied by time, and the unit step is the only place where a factor of a thousand can hide. Entering 1.5 in the kilowatts mode gives the same answer as entering 1500 in the watts mode, and both are correct.
From a daily figure to a yearly one
The daily figure is multiplied by 30 for a month and by 365 for a year. Nothing else changes between them — no seasonal adjustment, no rate change — so the three readings stay consistent with each other.
Fixed multipliers are a deliberate choice. Real months are 28 to 31 days and a real year is 365 or 366, but mixing those in would make the daily, monthly and yearly numbers stop agreeing with one another, and the first thing anyone does with a calculator like this is check that they multiply out.
The trade is worth stating plainly: the monthly figure is an average, not a prediction. If the appliance is a heater it will run far more in January than in July, so no single monthly number describes the whole year. What the figure is good for is comparison — two appliances in the same house, measured the same way, give a fair ranking.
What the yearly figure is really for is that ranking. A few cents an hour is impossible to weigh against a purchase price; a yearly total in your own currency is not. Once both appliances are expressed the same way, the decision usually makes itself.
Switching units has to change the number, not just the label
Turn 1500 W into kW and the figure has to become 1.5, not stay at 1500 with a new name attached. The unit switch on this page genuinely recalculates, because 1500 kW is a small power station, not a space heater.
Changing the label alone is the commonest bug in a form like this: the value stays put, the unit name changes, the result is off by three orders of magnitude, and the page looks perfectly normal. So a switch parses the old value into a base quantity and writes it back in the new unit, with the number moving.
Input that cannot be parsed, such as an empty field or letters, is left exactly as typed and handed to the calculation to report, rather than being quietly replaced with zero on the switch. Turning a bad input into a zero erases the problem the reader had just been shown.
The money figure itself carries no currency symbol: the symbol follows where you are, not the interface language. The same 0.35 is 0.35 euros in Germany and 0.35 yuan in China, and changing language must not change that number.
Frequently asked questions
How do I work out what an appliance costs to run?
Multiply the power in kilowatts by the hours it runs, which gives kilowatt hours, then multiply by your price per kilowatt hour. A 1,500 watt heater running four hours uses 6 kWh a day, so at 0.30 per kWh that is 1.80 a day. Extend it to a month and a year and the number stops looking small.
What exactly is standby power?
It is the power an appliance draws while it is switched off but still plugged in. Televisions, set-top boxes, games consoles, printers and anything with a remote control or a display all have some. It is usually only a few watts, which sounds trivial until you notice it runs 8,760 hours a year rather than the two or three hundred you actually use the device.
Where do I find the wattage?
On the rating plate, usually on the back or the underside, and in the manual. Note the difference between the rated power and the average power: a fridge or an air conditioner cycles on and off, so its average draw is well below its peak. For anything that cycles, the rated figure will overstate the running cost.
Is a kilowatt hour the same as a kilowatt?
No, and mixing them up is the most common mistake here. A kilowatt is a rate, like speed. A kilowatt hour is a quantity, like distance. A 1,000 watt appliance running for one hour uses exactly 1 kWh. Running the same appliance for half an hour uses 0.5 kWh, even though its rating is unchanged.
Why does the monthly figure use 30 days?
Because months differ in length and 30 is the round middle. Using one fixed number keeps the daily, monthly and yearly figures consistent with each other, so you can move between them by simple multiplication instead of re-deriving each one. The yearly figure uses 365 days and ignores leap years for the same reason.
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