Your electricity bill talks in kilowatt-hours. A physics problem, a battery spec sheet, or a science fair project talks in joules. They measure the same thing, energy, just at wildly different scales. 1 kWh = 3,600,000 joules, which is 3.6 megajoules. That’s a big jump, and this converter handles it instantly so you don’t fumble the zeros.
Where does that number come from? A kilowatt is 1000 watts (joules per second), and an hour is 3600 seconds. Multiply 1000 by 3600 and you get 3,600,000 joules in one kWh. So 2 kWh is 7,200,000 J, half a kWh is 1,800,000 J, and a 10 kWh figure balloons to 36,000,000 joules. The scale is exactly why nobody bills in joules.
The short version
- 1 kWh = 3,600,000 J = 3.6 MJ. Fixed factor, no offset.
- Multiply kWh by 3.6 million to get joules.
- Divide joules by 3.6 million to go back.
Type a kWh value and the joule result lands on the spot. Because the numbers get long, the tool keeps them readable, but the math underneath is just that single multiplier.
Where this comes up
Two worlds use these units, and converting bridges them.
Electricity bills and appliances. Your utility meters energy in kWh because joules would produce absurd numbers (a single kWh is already 3.6 million of them). A 2000 W heater run for one hour uses 2 kWh, or 7.2 million joules. Knowing the joule figure is handy when a homework problem or an engineering calc wants SI units instead of utility units.
Battery capacity. Battery and power station specs sometimes list energy in watt-hours or kWh, sometimes in joules, and occasionally you need to reconcile them. A 0.5 kWh portable power station stores 1,800,000 joules. Phone and laptop batteries are usually rated in watt-hours (a thousandth of a kWh), so a 50 Wh laptop battery is 0.05 kWh, or 180,000 joules.
Handy reference points
A few conversions to anchor the scale:
| kWh | Joules | Also |
|---|---|---|
| 0.001 (1 Wh) | 3,600 | 3.6 kJ |
| 0.1 | 360,000 | 0.36 MJ |
| 1 | 3,600,000 | 3.6 MJ |
| 5 | 18,000,000 | 18 MJ |
| 10 | 36,000,000 | 36 MJ |
The tool’s table mirrors this, and the free input takes any value with the megajoule equivalent shown alongside.
How to use it
Enter a kilowatt-hour value and the joule result updates instantly, no button. The reference table covers common amounts so you can often skip typing. Everything runs in your browser using the exact 3,600,000 factor, so nothing you enter gets uploaded and it works offline once the page loads.
FAQ
How many joules in a kWh?
Exactly 3,600,000 joules, which is 3.6 megajoules. It comes from 1000 watts times 3600 seconds in an hour.
Why is a kWh such a large number of joules?
Because a joule is a tiny unit (one watt for one second). An hour at a kilowatt is 3.6 million of those, which is why utilities bill in kWh rather than drowning your statement in zeros.
How do I convert kWh to megajoules?
Multiply by 3.6. One kWh is 3.6 MJ, so 5 kWh is 18 MJ. The tool shows the megajoule figure next to the joule result.
What’s a watt-hour in joules?
3600 joules. A watt-hour is a thousandth of a kWh, so it’s 3,600,000 divided by 1000. Laptop and phone batteries are usually rated in watt-hours.
Does this need internet?
No. It’s browser-side arithmetic with the factor built in, so it runs offline after loading and never sends your numbers anywhere.