How the electricity cost calculator works
Electricity is billed in kilowatt-hours (kWh): one kilowatt of power used for one hour. Convert the appliance's watts to kilowatts, multiply by hours of use, then by your rate.
Cost = kWh × Rate per kWh
Label wattage is the maximum. Appliances that cycle, like refrigerators, air conditioners and space heaters on a thermostat, use less on average, so a plug-in energy meter gives the most accurate figure. Find your rate by dividing the total on your bill (excluding fixed fees) by the kWh used. Standby or "vampire" power from devices that are off but plugged in typically adds 5 to 10% to home electricity use.
Worked example
A 1,500 W space heater running 3 hours a day uses 4.5 kWh daily, 135 kWh a month. At 17 cents per kWh that costs 77 cents a day, $22.95 a month and $275.40 a year. A 10 W LED bulb on for 5 hours a day costs about 26 cents a month.
Frequently asked questions
How do I calculate the cost to run an appliance?
Watts ÷ 1,000 × hours × your price per kWh.
How much does it cost to run a space heater?
A 1,500 W heater costs about 25 cents per hour at 17 cents per kWh.
What is a kilowatt-hour?
The energy used by a 1,000 W device running for one hour.
Where do I find my electricity rate?
On your bill: divide the energy charges by the kWh used, or look for the price per kWh line.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.