How to work out electricity cost
Energy (kWh) = power (W) × hours ÷ 1,000
Cost = energy (kWh) × price per kWh
Example
A 1,500 W heater used 3 hours a day uses 1,500 × 3 ÷ 1,000 = 4.5 kWh a day. At 0.20 per kWh that’s 0.90 a day, or about 27 a month.
Ways to cut the cost
- Switch off things on standby, or use a smart plug with a timer.
- Run washing machines and dishwashers full, and at night on cheaper night rates.
- Replace old bulbs with LEDs: they use about a fifth of the power.
Frequently asked questions
How do I find my appliance's wattage?
Look for a label on the back or bottom, or in the manual. It shows watts (W) or kilowatts (kW). If it only shows amps, multiply amps by your mains voltage (230 V in most of the world, 120 V in North America) to get watts.
Where do I find my price per kWh?
On your electricity bill, as the unit rate or energy charge per kilowatt hour. If you have different day and night rates, use the rate for when you run the appliance.
Why is my fridge's real cost lower than its wattage suggests?
Fridges, air conditioners and heaters switch on and off to hold a temperature, so they don't use full power all day. For those, use the average power from the energy label, or fewer hours a day.
Which currency does it use?
Any. Enter your price per kWh in your own currency, and the costs come out in the same currency.