Electricity cost calculators and guides for checking everyday usage assumptions.
Practical electricity calculator
Convert appliance wattage and a selected runtime into kWh before pricing the same period.
How to read the result
Watts tell you how much power an appliance draws while it is running. kWh tells you how much energy it uses over the time period you entered. That is the number you need when you want to compare usage with an electricity bill or estimate running cost.
Use the total kWh result when you want to move from "this appliance is 800 watts" to "this is how much energy it uses in a day, week, or month." Use watt-hours when comparing product specifications, small devices, battery sizes, or power-station capacity.
If the kWh result is higher than expected, check both runtime and quantity. One device used briefly may not use much energy, but several identical devices or long continuous runtime can change the total quickly. If you want the concept first, read Watts vs kWh Explained.
Use kWh when you want to compare energy use before thinking about price. Convert kWh into cost only after you have a rate per kWh that matches the period or device you are estimating.
Once you know kWh, use the kWh to Cost Calculator to estimate usage cost. If you still need watts, hours, and daily or monthly cost in one step, use the Appliance Electricity Cost Calculator.
Example
Suppose a fan is rated at 60 W and runs for 10 hours. The energy use is 0.6 kWh because 60 watts multiplied by 10 hours equals 600 watt-hours, or 0.6 kWh.
This kWh number is the bridge between the product label and your electricity cost. After converting the fan's wattage into kWh, you can use your electricity rate to estimate whether running it overnight is a small cost or something worth tracking over a month. For a night-by-night example, use the fan electricity cost overnight guide. For the full formula path, read How to calculate electricity cost from watts.
Example
A 25 W device running for 24 hours uses 0.60 kWh because 25 x 24 / 1000 = 0.60. This kind of conversion is useful when a low-wattage device has a clear always-on runtime and you need the kWh step before adding a rate.
Once you have the kWh value, use the kWh to Cost Calculator to turn the energy use into an estimated usage cost.
Common runtimes
These examples show how quickly runtime changes the kWh result before any cost is calculated.
Scroll horizontally to see all columns.
| Example | Watts | Runtime | Estimated kWh |
|---|---|---|---|
| Router and modem pair | 30 W | 24 hours | 0.72 kWh |
| Air purifier | 45 W | 10 hours | 0.45 kWh |
| Desktop work setup | 280 W | 7 hours | 1.96 kWh |
| Dishwasher cycle | 1200 W | 1.5 hours | 1.80 kWh |
Calculation logic
The calculation multiplies the wattage of the appliance by the number of hours it runs and by the number of identical appliances. It then divides by 1000 to convert watt-hours into kilowatt-hours.
Formula: kWh = (watts x hours x quantity) / 1000
Common uses
FAQ
Watts measure power, not total energy. kWh requires a time period because energy use depends on how long the appliance runs.
Yes. Enter a decimal such as 0.5 for 30 minutes or 1.25 for one hour and 15 minutes. Keep the entered period visible when you price the kWh result.
Enter the exact period you want to understand. A daily runtime produces daily kWh; a monthly runtime produces monthly kWh. Select the same period after the result moves to the kWh to Cost Calculator.
Rated wattage from the label or product page is a good starting point. If you have a plug-in power meter, measured wattage can give a more realistic estimate, especially for appliances with variable power modes. If you are not sure what wattage to enter, read How to find appliance wattage.