Electricity Cost Calculator
A 100 W device running 8 hours a day uses 0.8 kWh a day and 24 kWh in 30 days. At an example price of 0.15 per kWh that costs 3.60. Enter your own rate for a real figure.
How to use
- Enter the appliance power in watts. It is printed on the label or in the manual.
- Enter the hours it runs per day, the number of days, and how many identical appliances you have.
- Enter your price per kWh as a plain number without a currency symbol. Rates differ by country, region and plan, so take it from your own bill.
How it works
Energy in kilowatt-hours is watts × hours ÷ 1000, multiplied by the number of appliances. One kWh is 1000 W running for one hour.
Cost is kWh × price per kWh. The calculator multiplies the daily figure by the number of days you entered, by 30 for a month and by 365 for a year.
The result uses the power you enter as if the appliance drew it for every hour it runs. Many appliances cycle on and off (a fridge compressor, a heater with a thermostat), so their real average draw is lower than the label rating.
Worked examples
These use an assumed price of 0.20 per kWh purely to show the arithmetic. Replace it with your own rate.
| Case | kWh per day | kWh per 30 days | Cost per year |
|---|---|---|---|
| A 60 W device for 5 hours a day | 0.3 | 9 | 21.90 |
| A 1000 W device for 1 hour a day | 1 | 30 | 73.00 |
| A 10 W device left on all day | 0.24 | 7.2 | 17.52 |
Reading the result
- Doubling the hours or the number of appliances doubles the kWh and the cost.
- A small load that never switches off can add up. A 10 W device running all year uses 87.6 kWh.
- A plug-in power meter gives the real average draw of an appliance, which is more reliable than the label.
FAQ
What price per kWh should I enter?
The rate on your electricity bill, as a number without a currency symbol. If your bill has tiers or time-of-use rates, use the rate that applies to the hours the appliance runs, or an average. The calculator does not assume any country rate.
What is standby power?
Many devices keep drawing a small amount of power while switched off or idle, for example for a clock, a remote sensor or a network connection. To estimate it, enter the standby watts (a plug-in power meter can measure it) and 24 hours per day.
How do I find the watts of an appliance?
Check the rating label or manual. If it lists volts and amps instead, multiply them: watts = volts × amps. For a precise figure on a real appliance, use a plug-in power meter.
Why is my real bill different?
The label power is often a maximum. Appliances with motors, compressors or thermostats draw less on average, and bills also include fixed charges and taxes that this calculator leaves out.
Does the number of days change the monthly figure?
No. The month row always uses 30 days and the year row 365 days. The extra row for your own number of days appears only when it differs from 30.