Instantly convert energy units between kilojoules (kJ) and joules (J) with precise results. Ideal for scientific calculations, nutrition labeling, and physics applications.
Conversion Formula:
Joules = Kilojoules × 1000
International standard: 1 kilojoule (kJ) = 1000 joules (J)
Accepts decimal values (e.g., 2.5 kJ = 2500 J)
Precision:
Quick conversions - click to auto-fill:
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Converting between kilojoules and joules is straightforward thanks to their decimal relationship
The relationship between kilojoules and joules is based on the metric system's decimal prefixes:
1 kilojoule (kJ) = 1000 joules (J)
"Kilo-" is a metric prefix meaning one thousand
This simple decimal relationship makes conversions between these units extremely straightforward, with no complex formulas or approximation factors needed.
Use these simple formulas for conversions in either direction:
To convert kJ to J:
Joules = Kilojoules × 1000
Example: 3.8 kJ = 3.8 × 1000 = 3800 J
To convert J to kJ:
Kilojoules = Joules ÷ 1000
Example: 5200 J = 5200 ÷ 1000 = 5.2 kJ
For quick mental calculations, use these simple techniques:
Example: Food Energy Conversion
A food item containing 1500 kJ of energy has: 1500 × 1000 = 1,500,000 joules of energy.
This is equivalent to approximately 358.5 kilocalories (food calories).
Quick reference for frequently used energy measurements
| Kilojoules (kJ) | = | Joules (J) | Typical Application |
|---|---|---|---|
| 0.001 kJ | = | 1 J | Small electrical device |
| 1 kJ | = | 1000 J | Energy to lift 100kg 1m |
| 2.5 kJ | = | 2500 J | Energy in a small apple |
| 10 kJ | = | 10,000 J | Energy in a slice of bread |
| 50 kJ | = | 50,000 J | Energy in a boiled egg |
| 100 kJ | = | 100,000 J | Energy in a banana |
| 418.4 kJ | = | 418,400 J | 100 food calories (kcal) |
| 1000 kJ | = | 1,000,000 J | Energy in a chocolate bar |
All conversions are exact since 1 kJ = 1000 J by definition.
Common questions about converting kilojoules to joules
A joule is the SI unit of energy, work, or amount of heat. It is defined as the work done by a force of one newton acting over a distance of one meter. In everyday terms, one joule is approximately the energy required to lift a small apple one meter straight up.
Conversions between kilojoules and joules are commonly needed in:
The conversion is straightforward because the metric system uses prefixes to denote multiples of base units. "Kilo-" specifically means 1000, so a kilojoule is simply 1000 joules. This decimal-based system makes conversions between units a matter of moving the decimal point rather than using complex conversion factors.
Food energy is often measured in kilocalories (kcal), which are sometimes called "Calories" with a capital C. The conversion between food calories and joules is:
1 food calorie (kcal) = 4.184 kilojoules (kJ) = 4184 joules (J)
This is why you'll often see both kcal and kJ listed on nutrition labels.
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Convert kilojoules to joules instantly with our accurate online converter. Supports bidirectional conversion with formula, examples, and reference table.
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Convert kilojoules (kJ) to kilocalories (kcal) for food, diet, and fitness tracking—1 kcal = 4.184 kJ.
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Convert kcal to kJ (kilocalories to kilojoules) for food nutrition, diet, and fitness—1 kcal = 4.184 kJ.
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