What is a watts to kWh calculator?
A watts to kWh calculator turns a device’s power rating and how long it runs into the amount of energy it uses. Watts (W) describe how fast electricity is consumed at any instant, while a kilowatt-hour (kWh) measures the total energy used over time. Because electricity bills are charged per kilowatt-hour, this conversion tells you exactly how much energy an appliance draws during a given period.
Formula
Energy in kilowatt-hours equals power in watts multiplied by the running time in hours, divided by 1000 (since one kilowatt is 1000 watts):
How to use
- Enter the appliance’s power in watts — usually printed on a label or in the manual.
- Enter the running time in hours.
- Read the energy used in kilowatt-hours. The result appears automatically once both fields are filled.
Worked example
Suppose a 1000 W space heater runs for 5 hours:
For a smaller load, a 60 W bulb left on for 24 hours uses:
FAQ
How do I work out the cost from kWh? Multiply the kWh figure by your electricity price per kilowatt-hour. You can do this directly with the electricity cost calculator.
My appliance is rated in kilowatts, not watts. What do I do? Multiply the kilowatt rating by 1000 to get watts first, then use this calculator. The kilowatts to watts calculator handles that conversion for you.