Electricity Cost Calculator
See what it costs to run a single device per day, month, and year based on its wattage and your electricity rate.
Estimates only, not financial, tax, or legal advice. See our Terms and Privacy Policy.
Every electric device converts watts and hours into kilowatt-hours, the unit your utility actually bills you for. This calculator takes a device's wattage, how long you run it, and your electricity rate, then shows what it costs to run per day, month, and year.
It's a quick way to see which devices are actually driving up a bill, a space heater running all day costs far more than most people expect, while a phone charger costs almost nothing.
To estimate a full household bill across several devices at once, use this site's kWh Bill Estimator instead, which adds up multiple devices and includes a fixed base fee. Once you know the cost, fold it into your monthly budget alongside everything else.
How does this calculator work?
Enter the device's wattage, usually printed on a label, in the manual, or on the plug itself.
Enter how many hours per day it actually runs, not just how long it's plugged in.
Enter your electricity rate per kilowatt-hour, found on a recent utility bill.
The calculator first converts watts and hours into energy used: kWh per day = (watts × hours) ÷ 1,000. Dividing by 1,000 converts watt-hours into kilowatt-hours, the unit utilities actually bill in.
It multiplies that daily energy figure by your rate to get cost per day, then scales that same daily cost up to a month (× 30, a standard billing-cycle approximation) and a year (× 365) so you can see the same device's cost at whatever timeframe is useful to you.
See the Department of Energy's guide to estimating appliance energy use for this same formula, and check the EIA's average electricity prices by state if you want to sanity-check your own rate.
Worked example
A 100-watt light left on for 5 hours a day, on a $0.15 per kWh electricity rate.
- Energy used per day
- 0.5 kWh
- Cost per day
- $0.075
- Cost per month
- $2.25
- Cost per year
- $27.38
How the numbers work
100 watts times 5 hours is 500 watt-hours, or 0.5 kilowatt-hours, per day.
0.5 kWh times $0.15 per kWh is $0.075 a day, which adds up to $2.25 over a 30-day month and about $27 over a year.
One light bulb barely registers on a bill, but the same math applied to a 1,500-watt space heater running 8 hours a day (about $54 a month at this rate) shows why high-wattage devices used for long stretches are worth paying attention to.
Electricity Cost Calculator glossary
- Watt (W)
- A unit of power, how much energy a device draws at any given moment. Printed on most appliances and electronics.
- Kilowatt-Hour (kWh)
- The unit your electric bill is actually priced in: 1,000 watts running for 1 hour. It's the standard measure of energy used over time, not just power draw.
- Electricity Rate
- The price your utility charges per kilowatt-hour, shown on a bill, sometimes varying by time of day or total usage tier.
Electricity Cost Calculator FAQs
Where do I find a device's wattage?+
Check the label on the device itself, the box it came in, or the manual. Many devices list wattage directly; others list amps and volts, which you can multiply together (watts = amps × volts) to get the same figure.
Where do I find my electricity rate?+
Look at a recent bill for a line showing price per kWh, sometimes labeled "energy charge" or "supply rate." If your bill only shows a total dollar amount, divide the total by the kWh used that period to estimate your effective rate. Rates also tend to rise over time along with inflation generally.
See the Inflation CalculatorWhy use 30 days for the monthly estimate?+
It's a simple, commonly used approximation for a billing cycle. Actual billing cycles run 28 to 31 days depending on the month, so treat the monthly figure as a close estimate rather than an exact bill amount.
Does this account for devices with variable power draw?+
No, it assumes a constant wattage the whole time it's running. Devices like refrigerators, air conditioners, and heat pumps cycle on and off and draw variable power, so their real-world usage will differ from a flat wattage estimate. The kWh Bill Estimator lets you enter your best estimate of average running time to account for this.
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