What this calculator does
This tool tells you how much it costs to run an electrical device for one hour, based on the device's power rating in watts and the price you pay for electricity per kilowatt-hour (kWh). It also projects the cost over a day, a month and a year of continuous operation so you can spot energy-hungry appliances.
How to use it
Enter the device's power draw in watts — you'll usually find this on a label on the appliance or in its manual. Then enter your electricity rate per kWh, which appears on your utility bill (use your own currency; the result is in the same currency). Press calculate to see the running cost.
The formula explained
Electricity is billed per kilowatt-hour. Since 1 kilowatt equals 1,000 watts, you first divide the wattage by 1,000 to convert to kilowatts. Running that load for one hour consumes that many kilowatt-hours. Multiplying by your rate gives the hourly cost:
$$\text{cost per hour} = \frac{\text{watts}}{1000} \times \text{rate per kWh}$$
Worked example
Suppose a 1,500 W space heater and an electricity rate of $0.20 per kWh. Convert: \(1500 \div 1000 = 1.5\) kW. Multiply: $$1.5 \times \$0.20 = \$0.30 \text{ per hour}$$ Run it 24 hours and that's $7.20 per day, or about $216 per month.
FAQ
Where do I find the wattage? Check the rating label on the device, its power supply, or the manual. Amps × volts also gives watts.
Does it use real-time consumption? No — it assumes the device draws its rated power continuously. Devices that cycle on and off (like fridges) cost less than the headline figure.
What currency does it use? Whatever currency your kWh rate is in. The result comes out in that same currency.
