Electricity Calculator
Work out how much electricity an appliance uses and what it costs. Enter its wattage, the hours it runs each day, the days it runs each month and your rate per kWh. The calculator shows kWh and cost per day, per month and per year, with a year counted as 12 of your months.
$0.15 is an example. Replace it with the rate on your bill.
How to use the Electricity Calculator
- Enter your numbers in the Electricity Calculator above.
- Press the Calculate button to see the result.
- To try other numbers, change any value and press the button again.
The electricity cost formula
kWh used = (Watts × Hours) / 1000 · · · Cost = kWh × Rate
Divide the wattage by 1,000 to get kilowatts, multiply by the hours of use to get kWh, then multiply by your rate. The month multiplies a day by the days per month you enter, and the year multiplies the month by 12. Costs are rounded to the cent. Enter the rate in dollars, so 18 cents per kWh is 0.18.
Worked example
The fields start with a 1,500 W space heater running 8 hours a day for 30 days at an example rate of $0.15 per kWh. That is 1,500 × 8 / 1,000 = 12 kWh and $1.80 a day, 360 kWh and $54.00 a month, and 4,320 kWh and $648.00 a year. A 100 W lamp on for 5 hours a day for 30 days uses 100 × 5 × 30 / 1,000 = 15 kWh, which costs $2.25 a month at the same rate.
Frequently asked questions
What's my actual kWh rate?
Check your utility bill, and replace the $0.15 example with your rate. For a sense of scale, the US Energy Information Administration put the average US residential price for August 2026 at 18.16 cents per kWh, with Hawaii highest at 47.18 cents and Nevada lowest at 12.72 cents. These are preliminary figures from its Electric Power Monthly, Table 5.6.A. Rates change month to month and many bills add fixed charges, so your bill is the better guide.
Are appliance wattage labels accurate?
The label usually gives the most the appliance draws. Many draw less most of the time: a refrigerator switches its compressor on and off, and a computer draws more under load. A plug-in energy monitor measures the real use in kWh.
How is the yearly cost worked out?
The calculator multiplies the monthly figure by 12, so the year follows the days per month you enter. For an appliance you use every day, enter 30.4375 days, which is 365.25 / 12, to count a full year of days.