Appliance energy calculator
Every electricity bill is the sum of what each appliance uses. For anything that runs at a constant power — heaters, kettles, irons — the consumption is simply power × time. The calculator turns watts and hours into kWh per day and per month.
Multiply the monthly kWh by the price per kWh on your own bill to see the cost; tariffs differ too much between countries and suppliers to build one in.
Your measurements
Result
- Use per day
- 2.00 kWh
- Estimated use per month
- 60.0 kWh
For several appliances, add up the results. Multiply by your price per kWh to get the cost.
How the calculation works
- Use per day (kWh) = appliance power (W) × hours of use ÷ 1,000.
- Use per month = use per day × 30.
Worked example
A 2,000 W appliance (an electric heater or a kettle used often) running one hour a day uses 2 kWh a day, or 60 kWh a month.
What the calculator assumes
- The appliance is assumed to run at its rated power the whole time it is on — correct for resistive loads (heaters, kettles, irons).
- The power is on the appliance's rating plate or in the manual, in watts (W).
When to adjust the result
- Fridges, washing machines and air conditioners switch on and off by themselves; for them use the annual consumption on the energy label, divided by 12.
- For the whole home, add the appliances one by one — or compare with your meter readings over a week.
- Standby consumption (TV, set-top box, chargers) isn't included, but together it can add a few percent to the bill.
Finding where electricity goes
Big consumers are appliances that heat or cool: electric heating, water heaters, ovens, tumble dryers and fridges running all year. A plug-in energy meter shows the real consumption of a device over a day or a week, which is often different from the label.
Standby adds up across many devices — routers, TVs, chargers and boxes. Switchable socket strips help. When replacing appliances, compare the annual kWh on the energy label, not just the class letter, because classes are relative within a product group.
Frequently asked questions
How do I convert watts to kWh?
Multiply the power in watts by the hours of use and divide by 1,000. A 100 W appliance running 10 hours uses 1 kWh.
How much does it cost to run an appliance?
Multiply the kWh it uses by the price per kWh on your electricity bill, including any taxes shown per kWh.
How do I convert watts to kWh?
Watts × hours used ÷ 1,000. A 2,000 W heater running 3 hours uses 6 kWh.
Does standby really matter?
Each device draws little, but ten devices at a few watts each running all year can add up to tens of kWh.