About the Electricity Cost Calculator
This electricity cost calculator works out how many kilowatt-hours an appliance uses and what that costs, based on its power rating, how many hours a day it runs, and your electricity rate. It answers the practical question behind an unexpectedly high bill or a purchase decision: what is this thing actually costing to run, per day, per month and per year.
How to use the Electricity Cost Calculator
- 1
Enter the appliance's power rating in watts, found on its rating label or in its manual.
- 2
Enter roughly how many hours a day it actually runs.
- 3
Enter your electricity rate per kilowatt-hour, found on a recent bill.
- 4
Read the energy used and estimated cost across a day, month and year.
What people use it for
Finding what's driving a high electricity bill
Check the running cost of a heater, air conditioner or other high-draw appliance to see how much of a bill it's realistically responsible for.
Comparing appliances before buying
Compare the running cost of two appliances with different wattages over a year to see whether a more efficient model's higher price pays for itself.
Budgeting for seasonal usage
Estimate the added cost of running an air conditioner or heater through a hot or cold season by adjusting the daily hours to match expected use.
How the calculation works
Power in watts is first converted to kilowatts by dividing by 1,000, then multiplied by the hours run per day to get kilowatt-hours per day — the standard unit every electricity bill is priced in. That daily figure is then scaled up to a month or year and multiplied by the rate per kilowatt-hour to produce a cost. This is exactly the calculation a utility meter performs continuously, just applied here to a single appliance instead of an entire household.
Why this is an upper-bound estimate, not an exact reading
The calculation assumes the appliance draws its full rated power for every hour entered, but many common appliances don't work that way. A fridge or air conditioner cycles its compressor on and off to maintain a set temperature rather than running continuously at full power, and a rated wattage is often a maximum rather than a typical figure. Because of this, the estimate here tends to run slightly higher than what a plug-in energy meter would actually measure for cycling appliances, while it is close to exact for something with a genuinely constant draw, like a kettle or an incandescent bulb.
Tips
- For the most accurate figure on a specific appliance, a plug-in energy monitor measures real usage directly rather than relying on the rated wattage.
- Standby power, when an appliance is plugged in but switched off, is usually small but adds up across many devices left connected continuously — worth checking separately if a bill seems unexplained.
- Electricity rates often vary by time of day; using an off-peak rate for overnight appliance use can noticeably change the estimated cost.