How to use the electricity cost calculator
Enter the appliance's power in watts, or its volts and amps if that's what the label shows. Set how many hours a day and days a week it runs, and your electricity rate in cents per kWh. The calculator shows the energy used and the cost per day, month and year. It defaults to the latest US average residential rate from the Energy Information Administration; replace it with the rate from your own bill.
The formula
kWh per day = watts × hours ÷ 1,000
cost = kWh × rate (¢) ÷ 100
per year = per day × days per week × 52.14
Worked example: a 1,500 W space heater, 4 hours a day
- Energy: 1,500 × 4 ÷ 1,000 = 6 kWh per day.
- Cost: 6 × 18.16 ¢ = $1.09 per day.
- Per year, every day: 6 × 365 = 2,190 kWh, about $398; per month about $33.
Finding an appliance's real wattage
- The nameplate. Most appliances list watts, or volts and amps, on a label near the cord or on the back. Volts × amps gives an upper estimate of watts.
- A plug-in power meter measures what a plug-in device actually uses over days, which is the best figure for anything that cycles, like a fridge, dehumidifier or space heater on a thermostat.
- The EnergyGuide label on major appliances gives estimated kWh per year directly; multiply by your rate to compare models.
- Your utility's smart meter data often shows hourly use, so you can see the jump when a big appliance switches on.
Ways to cut the bill
- Target the big loads. Heating, cooling, water heating and drying clothes dominate most bills; small electronics rarely matter.
- Time-of-use rates: if your utility charges less at night, shifting laundry or EV charging can save more than replacing appliances.
- Standby power: a device drawing 5 W around the clock uses 44 kWh a year. Smart strips help with entertainment centers.
Questions people ask
How do I calculate electricity cost?
Multiply the appliance's watts by the hours it runs, divide by 1,000 to get kilowatt-hours, then multiply by your rate. A 1,500 W heater used 4 hours a day uses 6 kWh a day; at 18.16 cents per kWh that's about $1.09 a day, $33 a month and $398 a year.
How many kWh does a device use?
kWh = watts × hours ÷ 1,000. A 100 W TV on for 5 hours uses 0.5 kWh. If the label shows amps instead of watts, multiply amps by volts to estimate watts.
What is the average cost of electricity per kWh?
The U.S. Energy Information Administration put the national average residential price at 18.16 cents per kWh in August 2026 (preliminary). Rates vary widely by state and utility, from around 11 to over 40 cents, so use the rate on your bill.
Why is my appliance using less than its rated watts?
The label shows the maximum. Thermostats, compressors and heating elements cycle on and off, so a refrigerator or space heater on a thermostat averages well below its nameplate. A plug-in power meter gives the real figure.
How do I find my electricity rate?
Divide the energy charges on your bill by the kWh used, or check your utility's rate schedule. Include delivery charges if you want the full cost of each extra kWh.
Sources and assumptions
- U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A: average residential price 18.16 ¢/kWh, August 2026 (preliminary)
- kWh = W × h ÷ 1,000. A month is taken as 365 ÷ 12 = 30.42 days.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.