Electricity Cost Calculator (kWh Calculator)

About this tool

This electricity cost calculator turns an appliance's wattage and how long you run it into kilowatt-hours (kWh) and money. Enter the watts (or the volts and amps from the label), the hours per day, the days per week and the price you pay per kWh, and it shows the energy and cost per day, per month and per year. You can then add several appliances to a list to see a combined total. It works as a kWh calculator too: leave the price blank and only the energy figures are shown.

How to use it

1. Enter the power. Type the watts from the rating label, or switch to Volts × amps if the label only lists current. The example list fills in rough figures as a starting point.
2. Enter how long it runs: hours per day (decimals work, so 15 minutes is 0.25) and days per week.
3. Enter your price per kWh from your electricity bill, in dollars or your own currency, not cents. 0.15 means 15 cents per kWh.
4. Press Calculate, then Add to list to build up a whole room or household. Remove a row with its × button.

The formula

A watt is a rate of energy use. A kilowatt-hour is the energy used by 1,000 watts running for one hour, and it is the unit utilities bill in. The US Department of Energy gives the same three steps this calculator uses:

kWh per day  = watts × hours per day ÷ 1000
kWh per year = kWh per day × days used per year
cost         = kWh × price per kWh

Days used per year here is 365 × days per week ÷ 7, and a month is one twelfth of a year (about 30.4 days), so monthly figures are averages. If the label lists amps instead of watts, multiply: watts = volts × amps. The DOE notes that most US household appliances run on 120 volts, while large ones such as clothes dryers and electric cooktops use 240 volts. For motors and electronics, volts × amps can be higher than the real power drawn, so treat that result as an upper estimate.

Worked example

The calculator opens with a 1,500-watt appliance, the same wattage as the DOE's kettle example, used 3 hours a day, 7 days a week, at an example price of 0.15 per kWh:

• Per day: 1,500 × 3 ÷ 1,000 = 4.50 kWh, costing 4.50 × 0.15 = $0.68 (0.675 before rounding).
• Per year: 4.5 × 365 = 1,642.5 kWh, or $246.38.
• Per month: 1,642.5 ÷ 12 = 136.88 kWh, or $20.53.

Cut it to 5 days a week and the year drops to 1,173.21 kWh and $175.98. Switching to volts and amps, 120 V × 12.5 A gives the same 1,500 W. The DOE's own example is a 1,500 W kettle used an hour a day: 547.5 kWh a year, which is $60.23 at 11 cents per kWh.

The US Energy Information Administration reported an average US residential price of 18.31 cents per kWh for July 2026 (Electric Power Monthly, released September 24, 2026). At that rate the example appliance would cost $300.74 a year. Prices differ widely by state, utility, plan and season, so your bill is the number to use.

Standby power

The DOE points out that many appliances keep drawing a small amount of standby power when they are switched off. It suggests unplugging them or using a power strip with a switch to cut these loads. To estimate one, enter its standby watts with 24 hours a day and 7 days a week. A device drawing 5 W all the time uses 5 × 24 × 365 ÷ 1,000 = 43.8 kWh a year, or $6.57 at 0.15 per kWh. A plug-in power meter is the simplest way to measure standby watts.

Reading your electricity bill

• kWh used is the energy for the billing period, from your meter. Comparing it with the calculator's monthly total shows how much of the bill a device accounts for.
• Tiered rates charge one price per kWh up to a threshold and a different price above it, so the last kWh you use can cost more than the first.
• Time-of-use rates charge different prices at different times of day. Use the rate for the hours the appliance actually runs.
• Fixed charges, delivery fees and taxes are also on most bills. Dividing the total bill by kWh used gives an all-in price: a $120 bill for 800 kWh works out to 0.15 per kWh. That is useful for rough estimates, but the fixed part does not go away if you use less.

Common mistakes

• Mixing up kW and kWh. kW is how fast power is used; kWh is how much energy was used over time.
• Entering cents as dollars. 15 cents is 0.15, not 15.
• Using the label wattage for cycling appliances. Refrigerators, air conditioners and heaters with a thermostat switch on and off, so real use is often lower than watts × hours. Enter only the hours the device is actually drawing full power, or measure it.
• Ignoring settings. A heater or hair dryer on a low setting draws less than its maximum rating.

Use cases

• Checking what a space heater, dehumidifier or gaming PC adds to the monthly bill.
• Comparing an old appliance with a more efficient replacement at the same hours.
• Estimating running costs for a home office, a rental unit or a garage workshop.

For the electrical side, the Ohm's Law Calculator relates volts, amps, ohms and watts, and the Unit Converter handles other energy and power units. To compare a price in another currency, use the Currency Converter.