Watts to kWh Calculator
Watts measure power; kilowatt-hours measure energy used over time. Enter a wattage and how long it runs to get the energy in kWh and what it costs.
Change any number below — your result updates instantly, no button to click.
Your details
Results
Measure or improve the real-world result
These tools are relevant to the numbers above; you do not need them to use the calculator.
As an Amazon Associate we earn from qualifying purchases. We may earn a commission from links on this page, at no extra cost to you.
Not sure which plug-in monitor fits? Compare a display meter with a smart plugHow it works
Energy (kWh) = watts ÷ 1000 × hours. Cost = energy × rate. For example, a 1,000 W appliance running 3 hours uses 3 kWh.
Watts to kWh conversion chart
Energy changes with both wattage and time. The example cost column uses $0.17 per kWh; enter your own rate above for a local result.
| Power | Time running | Energy used | Cost at $0.17/kWh |
|---|---|---|---|
| 10 W | 24 hours | 0.24 kWh | $0.04 |
| 60 W | 5 hours | 0.30 kWh | $0.05 |
| 100 W | 8 hours | 0.80 kWh | $0.14 |
| 500 W | 4 hours | 2.00 kWh | $0.34 |
| 1,000 W | 3 hours | 3.00 kWh | $0.51 |
| 1,500 W | 2 hours | 3.00 kWh | $0.51 |
| 2,000 W | 1 hour | 2.00 kWh | $0.34 |
These examples assume the device holds the entered wattage for the whole period. Cycling and variable-speed appliances need an average or measured kWh value.
Worked example: a 1,500 W appliance for 2 hours
Convert 1,500 W to 1.5 kW, then multiply by 2 hours. The appliance uses 3 kWh.
At $0.17 per kWh, the energy cost is 3 × $0.17 = $0.51. A 1,000 W device running for 3 hours uses the same 3 kWh: lower power over more time can equal higher power over less time.
Turn one day into monthly or yearly energy
A 100 W device used 8 hours per day consumes 0.8 kWh per day. Over 30 days that is 24 kWh; over 365 days it is 292 kWh. At $0.17 per kWh, the annual energy cost is about $49.64.
Repeat-use estimates assume the same schedule every day. For seasonal or occasional equipment, multiply the one-session kWh by the actual number of uses instead.
Nameplate watts are not always average watts
A steady resistive heater or incandescent lamp can remain close to its rated input while operating. Refrigerators, air conditioners, pumps, computers, and variable-speed equipment change draw over time, so rated watts multiplied by clock hours can overstate or understate real energy.
When an energy label already gives annual kWh, use that value directly. For a plug-in appliance, accumulated kWh from a compatible electricity monitor over a representative cycle is usually more useful than one instant watt reading.
Sources used for assumptions: U.S. Energy Information Administration — Measuring electricity; U.S. Energy Information Administration — Kilowatthour glossary definition.
Frequently asked questions
How many watts in a kWh?
A kWh is 1,000 watts used for one hour — or any equivalent, like 500 W for two hours, or 2,000 W for 30 minutes.
How do I convert watts to kWh per day?
Multiply watts by the hours used per day, then divide by 1,000. A 60 W bulb on for 5 hours uses 0.3 kWh a day.
Why does my bill use kWh not watts?
You pay for total energy consumed over time (kWh), not the instantaneous power draw (watts).
How many kWh does a 100 W device use?
A 100 W device uses 0.1 kWh per hour, 0.8 kWh over 8 hours, or 2.4 kWh if it runs continuously for 24 hours.
Can I use the maximum watt rating?
It gives an estimate only. Cycling or variable equipment may average above or below one instant or maximum rating, so measured or label kWh is better when available.
Related calculators
kWh to Watts Calculator
Enter energy used in kilowatt-hours and the time period to calculate the average power in …
ConversionskWh to Wh Calculator
Kilowatt-hours and watt-hours are both units of energy. Enter any value in kWh to convert …
ConversionskW to kWh Calculator
Power (kW) is the rate of use; energy (kWh) is power used over time. This calculator conve…
AppliancesAppliance Running Cost Calculator
Any appliance — a fridge, heater, gaming PC or AC unit — costs money every hour it runs. E…