Energy Converter
Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts.
How it works
Energy is measured in joules in SI, and everything here converts through that. A joule is small — one watt sustained for one second — so practical units multiply it heavily.
The calorie on a food label is not the calorie in a physics textbook. A food Calorie is a kilocalorie, 1,000 small calories or 4,184 joules. Both are listed here separately, because a factor of a thousand in a nutrition calculation is not a rounding error.
A kilowatt-hour is the energy unit on your electricity bill: one kilowatt sustained for an hour, which is 3.6 million joules. That is why kWh is the practical unit for household energy and the joule is not.
The formula
kWh → kJ
kJ = kWh × 3,600
kJ → kWh
kWh = kJ ÷ 3,600
Any pair in this family
result = value × (factor of source ÷ factor of target)
Every unit is defined against the j, so any combination converts in one step.
Worked examples
| Scenario | Working | Result |
|---|---|---|
| 1 kWh to kilojoules | 1 × 3600 | 3,600 kJ |
| 1 food Calorie to joules | 1 kcal × 4184 | 4,184 J |
| 2,000 kcal daily intake | 2000 × 4.184 | 8,368 kJ |
When you'd use it
- Converting food energy between Calories and kilojoules
- Working out electricity usage from a kWh reading
- Converting heating or cooling figures in BTU
- Physics coursework needing joules
Common questions
Is a food Calorie the same as a calorie?
No — a food Calorie (capital C) is a kilocalorie, 1,000 physics calories. A 2,000 Calorie diet is 2,000 kcal, or about 8,368 kJ. Labels in some countries show kJ instead, which is why the numbers look so much larger.
How many joules are in a kilowatt-hour?
3,600,000 — one kilowatt (1,000 joules per second) sustained for 3,600 seconds. That is why the kWh, not the joule, is the practical unit for an electricity bill.
What is a BTU?
The British thermal unit, roughly the energy to raise one pound of water by one degree Fahrenheit — about 1,055 joules. It survives in heating, ventilation and air-conditioning ratings, particularly in the US.
Is anything I enter sent anywhere?
No. Every conversion runs in your browser, so nothing you type is uploaded, logged or stored. There is no account and no record of what you converted.