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Joules Converter
Converts any energy value between joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds and electronvolts.
Last updated: July 2026 · Free · No sign-up required
Results
Enter values above and click Calculate to see your result instantly.
Quick reference
| Unit | In joules |
|---|---|
| 1 calorie (thermochemical) | 4.184 J |
| 1 kilocalorie (food Calorie) | 4,184 J |
| 1 BTU | 1,055.06 J |
| 1 watt-hour | 3,600 J |
| 1 kilowatt-hour | 3,600,000 J |
| 1 foot-pound | 1.3558 J |
Interpretation guide
| Energy | Roughly equals |
|---|---|
| 100 J | Lifting 10 kg about 1 meter |
| 4,184 J (1 kcal) | One food Calorie on a nutrition label |
| 1 MJ | About 0.28 kWh — 17 minutes of a 1 kW heater |
| 3.6 MJ (1 kWh) | One unit on your electricity bill |
Formula & methodology
Formula: Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J)
- Your input is first converted to joules using exact SI factors.
- The joule value is then divided by each target unit's factor.
Worked example: 1,000 J = 0.239 kcal = 0.948 BTU = 737.56 ft⋅lb = 0.000278 kWh. Going the other way, 500 food Calories (kcal) = 2,092 kJ — the energy in a typical fast-food burger.
Frequently asked questions
How do I convert joules to calories?
Divide by 4.184 for thermochemical calories, or by 4,184 for kilocalories (the food Calorie). 1,000 J is 239 cal, or 0.239 kcal.
How many joules are in a kWh?
Exactly 3.6 million joules: 1 kW is 1,000 J/s, and an hour has 3,600 seconds, so 1 kWh = 1,000 × 3,600 = 3,600,000 J.
What is the difference between a calorie and a Calorie?
A small calorie (cal) is 4.184 J. The food Calorie with a capital C is actually a kilocalorie — 1,000 small calories or 4,184 J. Nutrition labels always mean kcal.
How do I convert joules to BTU?
Divide joules by 1,055.06. A 1,000 J burst is 0.948 BTU; a therm (100,000 BTU) is 105.5 MJ.
What is an electronvolt?
The energy an electron gains across 1 volt: 1.602 × 10⁻¹⁹ J. It's the working unit of particle physics — visible-light photons carry about 1.6–3.3 eV.
How do I calculate energy in joules from mass and velocity?
Kinetic energy: E = ½mv² with mass in kg and velocity in m/s. A 0.145 kg baseball at 40 m/s carries ½ × 0.145 × 1600 = 116 J. Once you have joules, this converter moves the result into calories, watt-hours, ft·lb, or BTU — 116 J is about 27.7 calories or 85.6 ft·lb.
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