Electricity Cost Calculator
Enter the power of an appliance in watts, the hours you use it each day you use it, how many days a week, and your electricity price per kWh. You get the cost per day, month and year.
Your numbers
How we calculate it
Energy per day of use in kilowatt hours is watts × hours ÷ 1,000. The cost per day is that times your price per kWh. The cost per year is the cost per day times the days of use per week times 52, and the cost per month is a twelfth of the year.
A 100 watt device running 8 hours a day uses 0.8 kWh a day. At 0.15 per kWh that costs 0.12 a day, 3.64 a month and 43.68 a year.
Assumptions and limits
- The watts on a label are the most the device draws. Devices that cycle on and off, such as fridges and heaters, use less on average.
- Your bill may also include standing charges, taxes and tiered prices that this calculator does not include.
- A year is taken as 52 weeks.
Frequently asked questions
How do I find how many watts my appliance uses?
Look at the label or the manual. It shows watts, or volts and amps, which you multiply to get watts. A plug in power meter gives a real measurement.
What is a kilowatt hour?
A kilowatt hour (kWh) is the energy used by a 1,000 watt device running for one hour. Electricity is billed by the kWh.
Where do I find my price per kWh?
On your electricity bill or your supplier’s tariff page. If the price changes by time of day, use an average or run the calculator for each rate.
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Worked example (a fixed example using the starting numbers, it does not change as you type)
Inputs: Power (watts) = 100; Hours used per day of use = 8; Days used per week = 7; Electricity price ($ per kWh) = 0.15.
- Cost per year $43.68
- Cost per month $3.64
- Cost per day of use $0.12
- Energy per day of use 0.800 kWh
- Energy per year 291.2 kWh
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