Why use 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.
Step by step
- 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.
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.
When you would reach for this
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.
Worth knowing
- 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.