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Practical electricity calculator
Convert appliance wattage and runtime into kWh so you can understand energy use before estimating electricity cost. This is useful when a product page lists watts but your utility bill and electricity rate are based on kWh.
Convert power to energy use
This calculator converts the wattage of one or more identical appliances into total energy usage over the number of hours you enter.
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 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 for routers, small pumps, chargers, or other low-wattage devices that run for long periods.
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.
| Example | Watts | Runtime | Estimated kWh |
|---|---|---|---|
| Small device for one day | 25 W | 24 hours | 0.60 kWh |
| Fan overnight | 75 W | 8 hours | 0.60 kWh |
| Desktop setup workday | 200 W | 6 hours | 1.20 kWh |
| Space heater evening | 1500 W | 3 hours | 4.50 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.
kW is power draw at a moment in time. kWh is energy consumed over time. A 1 kW appliance running for 3 hours uses 3 kWh.
Yes. Enter the number of hours for the period you want to measure. For example, use 24 hours for one day of continuous use or 720 hours for a simple 30 day month estimate.
No. This page only converts wattage and runtime into energy use. Use the related electricity cost calculators when you want to turn kWh into money, including the kWh to Cost Calculator.
Yes. Enter decimals for partial hours. For example, 30 minutes is 0.5 hours, and 15 minutes is 0.25 hours.
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.
Many batteries and portable power stations list capacity in watt-hours. You can compare that number with the calculator's watt-hour result to estimate how long a device might run, but real runtime can be lower because of efficiency losses.
Enter the appliance's daily runtime first, then multiply the result by about 30 for a simple monthly estimate. For a full cost estimate, use the related appliance electricity cost calculator.
Related tools
Choose the next calculator from the number you have now: watts, kWh, a one-hour check, or a full appliance-use estimate.
Home energy
What it shows
Estimate the daily, monthly, and yearly electricity cost of an appliance from its wattage, usage hours, and electricity rate.
Best for
Comparing the running cost of heaters, fans, computers, kitchen appliances, and other devices before you buy or leave them on every day.
Home energy
What it shows
Estimate how much an appliance costs to run for one hour, a typical 8-hour stretch, or a full 24-hour day.
Best for
Getting a quick hourly running-cost estimate before checking longer daily or monthly usage.
Home energy
What it shows
Convert a known kWh amount into estimated electricity cost using your rate per kWh.
Best for
Turning known energy use from a bill, meter, appliance estimate, or watts-to-kWh result into a practical cost estimate.
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