How to calculate electricity cost
kWh per day = Watts × Hours per day ÷ 1,000
Cost per day = kWh per day × Rate per kWh
Cost per month = Cost per day × 365 ÷ 12
Example: a 1,500-watt space heater running 6 hours a day uses 1,500 × 6 ÷ 1,000 = 9 kWh. At 18.2¢ per kWh that's $1.64 a day, about $49.82 a month and $597.87 a year.
Getting accurate numbers
- Watts: check the label on the back or bottom of the device, or the charger. If it lists amps, multiply amps by volts (120 in the U.S.).
- Cycling appliances: fridges, heaters with thermostats and AC units switch on and off, so they use less than their rated power for the hours they're "on". A plug-in power meter gives the real figure.
- Your rate: divide your bill's total by the kWh used to get the all-in rate, including delivery charges. Rates vary widely by state.
Next steps
Thinking about an electric car? Compare charging with a gas car's fuel bill in the fuel cost calculator, or check a gas car's real mileage with the MPG calculator.
Frequently asked questions
How much does it cost to run a space heater?
A 1,500-watt heater uses 1.5 kWh per hour, about 27¢ an hour at 18.2¢ per kWh. Six hours a day is about $50 a month.
How much electricity does a gaming PC use?
A gaming PC typically draws 300 to 600 watts while gaming. At 450 watts for 4 hours a day and 18.2¢ per kWh, that's about $10 a month.
What is a kWh?
A kilowatt-hour is 1,000 watts used for one hour. A 100-watt TV running for 10 hours uses 1 kWh.
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