How the electricity cost calculator works
Enter a device wattage, how many hours a day you use it, your electricity rate, and how many of them you have, and the tool works out the running cost per day, month, and year. It converts watts and hours into kilowatt hours, the unit your utility bills you for, then multiplies by your rate.
The energy cost formula
Energy in kilowatt hours equals watts divided by one thousand, times hours of use. Cost is that energy times your rate per kilowatt hour. So a 100 watt device run five hours a day uses half a kilowatt hour daily, which at sixteen cents costs about eight cents a day and roughly thirty dollars a year.
Finding a device wattage
Check the label on the device or its power supply, which usually lists watts or amps. If only amps are shown, multiply amps by your voltage to get watts. For devices that cycle on and off, like refrigerators, use their average rather than peak draw, or measure with a plug-in energy meter for accuracy.
Cutting standby and running costs
The biggest savings usually come from high wattage devices used for long periods, such as heaters, air conditioners, and water heaters. Many electronics also draw standby power around the clock, which adds up. Use the yearly figure to spot which devices are worth replacing with efficient models or switching off at the wall.
Frequently asked questions
How do I calculate electricity cost? Multiply watts by hours, divide by 1000 for kWh, then multiply by your rate.
How much does it cost to run a 100 watt device? About eight cents for five hours at a sixteen cent rate, near thirty dollars a year.
Where do I find a device wattage? On its label or power supply; if it lists amps, multiply by voltage.
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