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Electricity Cost Calculator

Work out how much electricity an appliance uses and what it costs to run each day, month and year, from its wattage, how long you use it and your price per kilowatt-hour.

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How to use the electricity cost calculator

  1. Pick an appliance from the list of typical wattages, or choose Enter my own wattage.
  2. For your own appliance, enter its power in watts, or switch to amps × volts if the label only lists current.
  3. Enter how many of them you run, for example 10 light bulbs.
  4. Enter the hours used per day and the days used per month.
  5. Enter your electricity price per kWh from your bill.
  6. Read the monthly cost, the energy in kWh, and the table of typical appliances at your price.

How electricity cost is calculated

Your utility bills you for energy, measured in kilowatt-hours (kWh). One kWh is 1,000 watts running for one hour, or 3.6 megajoules.

Power (W) = watts on the label, or amps × volts Energy per day = watts × number of units × hours per day ÷ 1,000 (kWh) Energy per month = energy per day × days used per month Energy per year = energy per month × 12 Cost = energy (kWh) × price per kWh

Amps × volts gives the apparent power. For heaters, kettles and bulbs it equals the real power. For motors and electronics the real power is a bit lower, so amps × volts gives a cautious, slightly high estimate.

Worked example

The defaults are a 1,500 W space heater used 4 hours a day, 30 days a month, at $0.18 per kWh:

  • Power: 1,500 W = 1.5 kW
  • Energy per day: 1.5 kW × 4 h = 6 kWh, costing 6 × $0.18 = $1.08
  • Energy per month: 6 kWh × 30 = 180 kWh, costing 180 × $0.18 = $32.40
  • Energy per year: 180 × 12 = 2,160 kWh, costing $388.80
  • Cost per hour of use: 1.5 kWh × $0.18 = $0.27

Switch to amps × volts with 10 A at 120 V and the power becomes 1,200 W: 1.2 × 4 × 30 = 144 kWh, or $25.92 a month. A 10 W LED bulb on the same schedule uses 1.2 kWh, about $0.22 a month.

Typical appliance wattages

Appliance Typical watts Cost per hour at 18¢/kWh
LED light bulb 10 W 0.2¢
Laptop 50 W 0.9¢
LED TV (55-inch) 100 W 1.8¢
Refrigerator (while running) 150 W 2.7¢
Microwave oven 1,100 W 19.8¢
Electric kettle or space heater 1,500 W 27¢
Clothes dryer (electric) 3,000 W 54¢
Central air conditioner 3,500 W 63¢
Electric water heater 4,500 W 81¢
EV charger (Level 2) 7,200 W $1.30

These are typical ratings, and your model may differ by a lot, so use the label when you can. The U.S. Energy Information Administration put the average residential price at 17.3¢ per kWh for 2025 and expects about 18.2¢ for 2026 (EIA Short-Term Energy Outlook, October 2026). Prices vary widely by state and by plan.

Getting a realistic estimate

The wattage on a label is the most the appliance draws. Many appliances don't run at full power the whole time. A refrigerator's compressor cycles on and off, so it might run a third to half of the day; enter 24 hours with its running watts and the estimate will be too high. Thermostat-controlled heaters, air conditioners and water heaters behave the same way. For these, a plug-in energy meter or the yellow EnergyGuide label (which lists yearly kWh) gives a better figure. Also remember standby power: TVs, consoles and chargers draw a few watts even when off, which adds up over a year.

Frequently asked questions

How do I find an appliance's wattage?

Look for a label or nameplate on the back, underside or power brick. It lists watts (W), or volts and amps, which you multiply together. A plug-in watt meter shows the real draw, including standby.

How much does it cost to run a space heater?

A 1,500 W heater uses 1.5 kWh each hour. At 18¢ per kWh that is 27¢ an hour, or $32.40 a month at 4 hours a day. If its thermostat cycles it off, the real cost is lower.

What is a kilowatt-hour?

A kilowatt-hour is the energy used by a 1,000 W device running for one hour, or a 100 W device for 10 hours. It is the unit on your electric bill.

Why is my bill higher than the calculator's estimate?

Bills add fixed monthly charges, taxes and delivery fees, and some plans charge more at peak times or for higher usage tiers. Divide your total bill by the kWh used to find your true average price, and enter that.

Related calculators

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  • Voltage Drop Calculator — Voltage drop, percent drop and voltage at the load for copper or aluminum wire, AWG or mm², single- or three-phase.
  • BTU Calculator — Rule-of-thumb air conditioner size in BTU/h and tons for a room, with a rough heating estimate.

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