Electricity Cost Calculator

How electricity cost is calculated

Your utility charges for energy in kilowatt-hours (kWh). One kWh is 1,000 watts used for one hour. To find the cost of running an appliance, convert its power to kilowatts, multiply by the hours it runs, and multiply by your price per kWh. The calculator does this for a day, a week, an average month (365 ÷ 12 = 30.4 days) and a year.

Energy (kWh) = watts × hours ÷ 1,000
Cost = kWh × price per kWh
Monthly cost = daily kWh × 365 ÷ 12 × price

Worked example: a space heater

A 1,500 W space heater runs 6 hours a day and electricity costs $0.17 per kWh.

• Energy per hour of use: 1,500 ÷ 1,000 = 1.5 kWh, costing about $0.26.
• Per day: 1.5 × 6 = 9 kWh = $1.53.
• Per month: 9 × 30.4 = 273.75 kWh = $46.54.
• Per year, if used every day: 3,285 kWh = $558.45.

A 900 W window air conditioner running 8 hours a day at the same price uses 7.2 kWh a day and costs about $37.23 a month. Ten 10 W LED bulbs lit 5 hours a day in the UK at £0.25 per kWh cost only about £3.80 a month.

Where to find the wattage

• The rating label on the back or underside of the appliance, or the power adapter, lists watts (W) or volts and amps. If you only have amps, multiply by the voltage (120 V in North America, 230–240 V in the UK, Europe and Australia) or use the watts to amps calculator.
• Energy labels, such as the US EnergyGuide or the UK/EU energy label, give an estimated yearly kWh for fridges, freezers, washers and TVs. For those, yearly kWh × price is usually more accurate than watts × hours.
• A plug-in energy monitor measures what the appliance really uses, which is the best option for anything that cycles on and off.

The appliance list in the calculator gives example wattages as a starting point. Real products vary widely by size, age and setting, so replace the value with the figure from your own label whenever you can.

Appliances that cycle on and off

Refrigerators, freezers, air conditioners, heaters with thermostats and dehumidifiers do not draw their full rated power all the time: the compressor or element switches on and off. For these, either use the average draw (the yearly kWh from the label divided by 8,760 hours) with 24 hours a day, or use the full rated watts with the number of hours it actually runs. Entering the label wattage with 24 hours for a fridge would overstate the cost several times.

Finding your price per kWh

Divide the energy charge on your bill by the kWh used, or look for the unit rate. Many bills also have a fixed daily or monthly charge (called a standing charge in the UK, a supply charge in Australia) that you pay regardless of use; leave it out when costing a single appliance, and use the electric bill calculator to include it for the whole home. If you have time-of-use pricing, use the rate for the hours the appliance actually runs.

Ways to cut the cost

• Heating and cooling are usually the biggest loads. Lowering a thermostat setting or heating only the room you use saves far more than switching off chargers.
• Replacing older bulbs with LEDs cuts lighting energy dramatically for the same light.
• Run dishwashers, dryers and EV charging in off-peak hours if your tariff is cheaper at night.
• Check standby power: devices left on standby all year can add up, which a plug-in monitor will reveal.

Common mistakes

• Confusing watts and kWh. Watts is the rate of use; kWh is the amount used over time.
• Using the maximum rating for cycling appliances. See the section above.
• Forgetting quantity. Ten bulbs use ten times the energy of one; use the quantity field.

Estimates only. Your meter and bill show what you actually used.

Frequently asked questions

Sources

• US Energy Information Administration (eia.gov). Electricity explained: how electricity is measured and priced.
• Federal Trade Commission. EnergyGuide labels for home appliances.
• Ofgem (UK). Energy price cap: unit rates and standing charges.

Last reviewed 27 October 2026. Results are estimates; see our disclaimer.