About the Watts to kWh Calculator
This calculator converts W to kWh. W is one joule of energy per second, the basic unit of power printed on bulbs, chargers and appliances, and kWh is one kilowatt of power used for one hour, the unit your electricity meter counts and your bill charges for. It multiplies the wattage by the running time and divides by 1,000, then shows watt-hours, kilowatts and the cost if you give a price. Enter your figures and the answer appears at once, together with a few related values, and you can copy the result with one tap. The sums are done in your browser and nothing is sent anywhere.
Updated October 2026
How to use the Watts to kWh Calculator
- 1Enter the value in W.
- 2Fill in the other boxes that the W to kWh calculation needs, such as time, voltage or power factor.
- 3Read the answer in the large result box.
- 4Check the extra rows for related values.
- 5Press Copy result to keep it.
When you need W to kWh
Small appliances, chargers and bulbs are rated in watts, but your bill is in kilowatt-hours. This calculator bridges the two. A 60 W television on for five hours a day uses 0.3 kWh each day, and about 9 kWh in a month. Totalling devices this way shows where electricity really goes.
It is also the quickest check for off-grid and caravan power: if the lights, a fridge and a laptop use a certain number of watt-hours a day, you can size a battery and solar panel from the total. Add a price per kWh and the cost of each device appears too.
How the W to kWh sum works
kWh = watts × hours ÷ 1,000. A 100 W lamp left on for 24 hours uses 100 × 24 ÷ 1,000 = 2.4 kWh.
The displayed answer is rounded to six significant figures, but the sum itself is not rounded, so converting W to kWh and back again gives you the number you started with.
- Use realistic hours of use
- Standby power adds up over a month
- Compare devices by kWh a year
Mistakes to avoid when converting W to kWh
The classic error is forgetting to divide by 1,000 when moving from watt-hours to kilowatt-hours. Another is using the rating of a device that does not run continuously, such as a kettle or a fridge compressor. Use the realistic number of hours of use.
On phone and computer
On a phone, type in the boxes one after another and read the kWh result underneath; the Copy button puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the kWh value move. The W to kWh page works the same on both. For round numbers in kilowatts, kW to kWh Calculator is faster. kWh to Watts Calculator reverses the step, Electricity Cost Calculator adds a price, and Ohm's Law Calculator links power with voltage and current.
Features
- W to kWh in one step
- Related values shown with the answer
- Clear messages for impossible inputs
- Copy the result with one tap
- Private: nothing is uploaded
- Works on phone and computer
Frequently asked questions
How do I convert W to kWh?
kWh = watts × hours ÷ 1,000. A 100 W lamp left on for 24 hours uses 100 × 24 ÷ 1,000 = 2.4 kWh.
What is the formula for W to kWh?
kWh = watts × hours ÷ 1,000. The calculator applies it exactly and rounds only the displayed answer.
What is the difference between W and kWh?
W is one joule of energy per second, the basic unit of power printed on bulbs, chargers and appliances. kWh is one kilowatt of power used for one hour, the unit your electricity meter counts and your bill charges for. They measure different things, which is why converting from W to kWh needs more than a simple multiplication in some cases.
How many kWh does a 100 watt bulb use in an hour?
0.1 kWh. A 100 W bulb running for 10 hours uses 1 kWh.
Can I include the cost?
Yes. Enter the price you pay per kWh and the cost is added below the energy figure.
Is this W to kWh calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so the figures you type are not uploaded or stored. It is meant for planning and learning; for wiring or safety work, check the result against your equipment's rating plate and local rules.