Appliance energy calculator
Enter the power of the appliance while it runs, how long and on how many days a week you use it, its standby power and your electricity price. You see the yearly kWh and cost and how much of it is spent just sitting on standby.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the running power in watts, the hours you use it per day and the days per week.
- Enter the standby power in watts (0 if it is truly off at the wall or has none).
- Enter what you pay per kWh in your own currency.
How it works
Running hours per year = hours per day × days per week × 365 ÷ 7. Running energy = watts × running hours ÷ 1,000. Standby energy = standby watts × (8,760 − running hours) ÷ 1,000. Cost = kWh × price. The monthly figure is a twelfth of the yearly one.
Worked example
A 120 W device used 5 hours a day, 7 days a week, with 3 W standby at 0.16 per kWh: running 120 × 1,825 h = 219 kWh; standby 3 W × 6,935 h = 20.8 kWh; total 239.8 kWh, so about 38.37 per year or 3.20 per month. Standby is about 9% of the total.
Tips
- Real consumption varies with load: a fridge, heater or compressor cycles on and off, so measure it if you can.
- Unplugging devices or using a switched power strip removes standby draw.
- Use an energy meter reading for the most accurate wattage.
Frequently asked questions
How do I find an appliance's wattage?
Look for the rating label on the back or underside, or the manual. A plug-in energy meter shows the real draw, including standby, which is more accurate because many devices draw less than their label rating most of the time.
What is standby power?
The small amount of electricity a device uses while it is switched off but plugged in, or waiting in a low-power mode. It runs all the hours the appliance is not in use, so a few watts add up over a year.
How is the standby energy calculated?
Standby watts multiplied by every hour of the year the appliance is not running (8,760 hours in a year minus the running hours), divided by 1,000 to give kWh.
How does this differ from the electricity cost calculator?
This one counts days per week and standby for the rest of the time, for a single appliance. The electricity cost calculator offers typical wattages and works per day, month and year.