Convert energy units — joules, calories, kilowatt-hours, BTU, kilojoules.
| Unit | Name | Value |
|---|---|---|
| J | Joule | 1000 |
| cal | Calorie | 239.00574 |
| kcal | Kilocalorie (Cal) | 0.23900574 |
| kWh | Kilowatt-hour | 0.00027777778 |
| BTU | BTU | 0.94781339 |
Formula: Calorie = Kilojoule × 239
Multiply any kilojoule value by 239 to get calorie.
Reverse: Kilojoule = Calorie × 0.004184
Common kilojoule values — factor: 1 kJ = 239 cal
| Kilojoule (kJ) | Calorie (cal) | Context |
|---|---|---|
| 0.001 kJ | 0.239 cal | 1 J |
| 0.01 kJ | 2.39 cal | 10 J |
| 0.1 kJ | 23.9 cal | 100 J |
| 1 kJ | 239 cal | 1 kJ |
| 4.184 kJ | 1,000 cal | 1 kcal |
| 10 kJ | 2,390 cal | 10 kJ |
| 100 kJ | 2.39e+04 cal | 100 kJ |
| 1,000 kJ | 2.39e+05 cal | 1 MJ |
| 3,600 kJ | 8.604e+05 cal | 1 kWh |
| 1e+04 kJ | 2.39e+06 cal | 10 MJ |
| 1e+05 kJ | 2.39e+07 cal | 100 MJ |
| 1e+06 kJ | 2.39e+08 cal | 1 GJ |
| 1e+08 kJ | 2.390e+10 cal | 100 GJ |
| 1.000e+10 kJ | 2.390e+12 cal | 10 TJ |
| 1.000e+12 kJ | 2.390e+14 cal | 1 PJ |
1 kJ = 239 cal. Memorize for instant estimates.
Use 239 as a quick mental multiplier.
Multiply result by 0.004184 to recover the original kJ value.
Labels food energy in kJ for metric-market nutritional information.
Calculates reaction heat, enthalpy changes, and process energy in kJ.
Measures athlete metabolic rate and substrate oxidation in kJ.
Teaches heat transfer, steam tables, and engine cycles using kJ.
Prescribes energy intake using kJ in countries using metric labels.
Calculates heat duty for reactors, heat exchangers, and distillation in kJ.
The kilojoule (kJ) equals 1,000 joules and is the practical energy unit for food, chemistry, and heating applications in metric countries. Food energy labels in Australia, Europe, and most of the world use kilojoules.
A dietary calorie (kcal) equals 4.184 kJ. A can of soda contains about 600 kJ. The specific heat of water (4.184 kJ/kg·°C) means heating 1 liter of water by 1°C requires 4.184 kJ.
Interesting fact: An average adult needs about 8,000-10,000 kJ (2,000-2,400 kcal) per day. Running a marathon burns approximately 12,500 kJ.
The calorie (cal) was defined in 1824 as the heat needed to raise 1 gram of water by 1°C. There are two versions: the small calorie (cal = 4.184 J) and the large calorie or kilocalorie (kcal = 4,184 J), which is the 'Calorie' used in nutrition.
The calorie remains standard in chemistry for heat of reaction measurements. In the US, food packaging uses 'Calories' (with capital C) which are actually kilocalories — a persistent source of confusion.
Interesting fact: The confusion between cal and kcal means that a food label saying '200 Calories' actually means 200 kcal = 200,000 cal = 836,800 joules. The SI unit for food energy is the kilojoule.
Converting kilojoule to calorie is common across energy, nutrition, engineering, and science. Different sectors use different energy units — joules in physics, kcal in nutrition, kWh in electricity, and BTU in HVAC — making accurate conversion essential for cross-disciplinary work and international comparisons.
Quick reference: 5 kJ = 1195 cal and 10 kJ = 2390 cal. Reverse: 1 cal = 0.004184 kJ. Exact factor: 1 kJ = 239 cal.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.