Electricity Cost Calculator

How to work out what an appliance costs

Electricity is sold by the kilowatt-hour (kWh): one kilowatt, 1,000 watts, used for one hour. Every cost figure comes from three steps, and the tool prints each one with your numbers in it:

1. Energy per day = watts × hours per day ÷ 1,000. A 1,500 W load used for 1 hour is 1.5 kWh.
2. Energy per year = energy per day × days used per year. Over 365 days that is 547.5 kWh.
3. Cost = energy × rate per kWh. The month figure is the year divided by 12.

The Department of Energy and Virginia Tech Extension publish the same method. Their worked examples are the tests this tool has to match: the kettle in the FAQ above, and a paper shredder drawing 3 A at 120 V for 15 minutes a day on 52 days, which is 4.68 kWh and about 51 cents at 11 cents per kWh.

Where the watts come from

Type the watts from the label or the manual. If the label prints amps, switch to Amps and pick 120 or 240 V: watts = volts × amps. The tool carries no list of typical appliance wattages. Makers publish different numbers for the same kind of device, and a wrong preset gives a confident wrong answer. A plug-in space heater on high is often 1,500 W, and a water-heater element is often 4,500 W, but your own label wins.

Time, share of time and standby

Time used per day takes hours, minutes, or a clock form like 1:30. Days used a year lets a device that runs only in winter, or only on weekdays, count for fewer than 365 days.

Share of time running matters for anything with a thermostat. A heater set to hold a room at one temperature might run half the time it is switched on, and a fridge cycles all day. Leave it at 100 for a lamp or a kettle. If you do not know the share, a plug-in meter over a few days tells you the real kWh, and an EnergyGuide label gives a yearly kWh for many appliances.

Standby watts are charged for the hours the device is not in use. Leave it at 0 unless you have measured it.

Which rate to use

The rate box starts at the US average and the state list fills it for any state. Both come from the Energy Information Administration (EIA), and the period is shown beside every rate, because prices change. The figure is an average for residential customers, so your own rate can sit above or below it.

For a closer number, use your bill. Divide the total by the kWh on it, and the result already includes delivery charges and fixed fees. The helper under the rate box does this for you and fills the rate. The cost of a device is then your own rate times its kWh.

Monthly bill card

The Monthly bill card turns the kWh on your bill into a cost: kWh × rate, plus a fixed charge if you have one. Use it to test a different rate, or to see what an extra 100 kWh adds. It does not know about tiers, time-of-use pricing or demand charges, which depend on the utility.

Common mistakes

• Using label watts for a device that cycles. Heaters, fridges and air conditioners do not run flat out all day.
• Counting hours on, not hours running. Use the share-of-time box for the difference.
• Forgetting delivery charges. Your rate per kWh on the bill is higher than the supply charge alone.
• Mixing cents and dollars. 18.19 cents per kWh is 0.1819 dollars. The tool has a switch for each.

Worked example

1. Inputs: 1,500 W, 1 h a day, 365 days a year, 18.19 ¢/kWh, US average, EIA January-July 2026 (preliminary).
2. Energy per day = watts × hours ÷ 1,000 = 1,500 W × 1 h ÷ 1,000 = 1.5 kWh
3. Energy per year = energy per day × days = 1.5 kWh × 365 = 547.5 kWh
4. Cost per year = energy per year × rate = 547.5 kWh × $0.1819 = $99.59
5. Cost per month = energy per year ÷ 12 × rate = 547.5 kWh ÷ 12 × $0.1819 = $8.30

Questions people ask

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