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Electricity Cost Calculator

Estimate how much electricity a device uses and what it costs per day, month and year. Enter its power, hours of use and your price per kWh, add standby power if you like, and compare with common household devices.

  • Free, no sign-up
  • Runs in your browser
  • Everyday
Usually printed on the device label or charger.
Unit
From your electricity bill, in your own currency, e.g. 0.15.
Used for the remaining hours of each day of use.

Results are estimates. A year is 12 months of use. Real bills add fixed charges, taxes and tiered or time-of-use prices.

How to use the electricity cost calculator

  1. Enter the device power and choose watts or kilowatts. You can usually find it on the label, the power adapter or in the manual.
  2. Enter the hours used per day, from 0 to 24. Decimals are fine, so 30 minutes is 0.5.
  3. Enter the days used per month. It starts at 30 for a device used every day.
  4. Enter the price per kWh from your electricity bill, in your own currency, for example 0.15.
  5. Optionally enter the standby power in watts: what the device draws when it is switched off but still plugged in. It is counted for the remaining hours of each day of use.
  6. Press Calculate.

The result shows the cost per day, month and year and the energy used in kilowatt-hours (kWh). The Details table then shows what a set of common devices would cost with the same hours, days and price, so you can compare.

The formula

Energy is power multiplied by time. Because prices are per kilowatt-hour, watts are divided by 1,000:

  • kWh per day = (power in W × hours + standby W × (24 − hours)) ÷ 1,000
  • kWh per month = kWh per day × days used per month
  • kWh per year = kWh per month × 12
  • Cost = kWh × price per kWh, rounded to 2 decimals

Worked example

A 1,500 W space heater runs 4 hours a day, every day (30 days a month), and electricity costs 0.15 per kWh.

  • Per day: 1,500 × 4 ÷ 1,000 = 6 kWh, costing 6 × 0.15 = 0.90.
  • Per month: 6 × 30 = 180 kWh, costing 27.00.
  • Per year: 180 × 12 = 2,160 kWh, costing 324.00.

A 100 W TV watched 5 hours a day that draws 2 W on standby uses 0.5 kWh while on and 2 × 19 ÷ 1,000 = 0.038 kWh on standby, 0.538 kWh a day in total. At 0.20 per kWh that is about 3.23 a month.

Good to know

  • These are estimates. The power on a label is often the maximum; many devices use less most of the time.
  • Fridges, freezers, air conditioners and heaters with a thermostat switch on and off, so their average draw is lower than their rated power. For a fridge, use its yearly kWh rating if it has one.
  • Real bills include fixed charges, taxes and sometimes tiered or time-of-use prices, so the cost per kWh on your bill may vary.
  • A year is counted as 12 months of the days you entered, so 30 days a month gives 360 days of use.

Frequently asked questions

How do I find out how many watts a device uses?

Look for a label on the back or bottom of the device or on its power adapter; it often shows watts (W) or volts and amps. Multiply volts by amps for an approximate wattage. A plug-in energy meter gives the most accurate reading.

What is a kilowatt-hour?

A kilowatt-hour (kWh) is the energy a 1,000 W device uses in one hour. A 100 W bulb takes 10 hours to use 1 kWh. Electricity bills charge per kWh.

What is standby power?

Many devices keep drawing a small amount of power when switched off but still plugged in, for example to power a clock or wait for a remote control. It is often between 0.5 and 5 W, but it adds up over a year across many devices.

Why does my bill not match the result?

The calculator looks at one device using its rated power. Your bill covers every device in the home plus fixed charges and taxes, and many devices draw less than their rated power on average.