Electricity cost calculator
Enter the power of a device in watts, how many hours a day it runs and what you pay per kWh. The calculator gives the energy and cost per day, month and year. You can also pick a common appliance to use a typical wattage, which is only an estimate: check the label or a plug-in energy meter for your own device.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Pick a device for a typical wattage, or choose Custom and enter the watts printed on the label.
- Set the hours of use per day and the number of devices.
- Enter your price per kWh from your electricity bill.
- Read the cost and energy per day, month and year.
kWh per day = watts × hours × devices ÷ 1,000. Cost = kWh × price per kWh. A year is 365 days and a month is a twelfth of a year.
Worked example
A 1500 W space heater runs 2 hours a day at a price of 0.20 per kWh. It uses 1500 × 2 ÷ 1,000 = 3 kWh a day, which costs 0.60. Over a year that is 3 × 365 = 1,095 kWh and 219.00. Per month it is 91.25 kWh and 18.25.
Tips
- The label power is the maximum. A thermostat-controlled heater or a fridge runs part of the time, so lower the hours to the real time it is on.
- Lighting and standby loads look small, but they run for many hours a year.
Frequently asked questions
How do I calculate the cost of running a device?
Multiply watts by hours and divide by 1,000 to get kWh, then multiply by your price per kWh. A 100 W device used 4 hours a day uses 100 × 4 ÷ 1,000 = 0.4 kWh a day. At 0.15 per kWh that costs 0.06 a day.
Where do I find my price per kWh?
It is on your electricity bill, usually as a unit rate. If your bill has a fixed charge and a unit rate, enter only the unit rate here. The calculator does not know your currency, so the cost is in whatever currency you entered.
Are the device wattages accurate?
No. They are typical figures for illustration. Real power depends on the model, age and how you use it. Heaters, ovens and fridges also cycle on and off, so the average draw is lower than their label while running. Use the rating label or a plug-in energy meter for a precise number.
How are the month and year calculated?
A year is 365 days of the daily use, and a month is one twelfth of a year (30.4 days). Seasonal use, such as heating, needs hours averaged over the full year.
Does standby power count?
Only if you include it. Devices left plugged in draw a few watts even when off. To model that, add a second device with a few watts and 24 hours a day.