1 Kilojoule = 1,000 Joules (10³ J) | SI Energy Unit
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SI base unit of energy (1 J = 1 N·m) | Used for physics, chemistry, nutrition
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J → kJ: kJ = J ÷ 1,000
kJ → J: J = kJ × 1,000
The joule is the SI base unit for energy, and "kilo-" is a metric prefix meaning 1000. This follows the standard metric system rule for SI units: adding "kilo-" multiplies the base unit by 1000 (e.g., 1 kg = 1000 g, 1 km = 1000 m, 1 kJ = 1000 J).
- Joules (J): Small energy measurements (e.g., kinetic energy of a ball, electrical energy in small circuits)
- Kilojoules (kJ): Larger energy values (e.g., food energy, mechanical work in engines, household electricity use)
For context: A 100W light bulb uses 100 J/s (0.1 kJ/s) of energy.
Divide by 1000: 250.5 ÷ 1000 = 0.2505 kJ. For easier calculation, move the decimal point 3 places to the left: 250.5 → 0.2505. For reverse conversion (0.75 kJ to J), move the decimal 3 places right: 0.75 → 750 J.
- 1 small calorie (cal) = 4.184 J = 0.004184 kJ (heat needed to raise 1g water 1°C)
- 1 food calorie (kcal / Cal) = 1000 small calories = 4184 J = 4.184 kJ
This is why nutrition labels use kJ (or kcal) to represent food energy (e.g., a banana has ~385 kJ / 92 kcal).
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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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Free online Joule to Kilojoule converter (1 kJ = 1000 J). Ideal for physics experiments, energy calculations, nutritional calorie conversion, and engineering work.
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