Joules to Kilocalories Converter (J to kcal)

Convert energy between joules (J) and kilocalories (kcal) instantly. Supports scientific notation, reverse conversion, and a quick reference table.

Joules ⇄ Kilocalories Calculator

You can use scientific notation (e.g. 2.5e6 for 2,500,000).

Conversion direction

Result

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Joules (J) Kilocalories (kcal)

How to convert joules to kilocalories

Joules (J) are the SI unit of energy, while kilocalories (kcal) are widely used in nutrition and older scientific literature. The relationship between them is defined exactly:

1 kilocalorie (kcal) = 4184 joules (J)

To convert from joules to kilocalories, divide by 4184. To convert from kilocalories to joules, multiply by 4184.

Formulas

Ekcal = EJ ÷ 4184

where EJ is energy in joules and Ekcal is energy in kilocalories.

EJ = Ekcal × 4184

where Ekcal is energy in kilocalories and EJ is energy in joules.

Example: 10,000 J to kcal

  1. Write the value in joules: 10,000 J.
  2. Use the formula: Ekcal = EJ ÷ 4184.
  3. Compute: 10,000 ÷ 4184 ≈ 2.389.
  4. Rounded to 2 decimals: 10,000 J ≈ 2.39 kcal.

Example: 500 kcal to joules

  1. Write the value in kilocalories: 500 kcal.
  2. Use the formula: EJ = Ekcal × 4184.
  3. Compute: 500 × 4184 = 2,092,000 J.
  4. So 500 kcal = 2,092,000 J.

Joules vs kilocalories: what’s the difference?

  • Joule (J) – SI unit of energy. Used in physics, engineering, and many scientific fields.
  • Calorie (cal) – energy needed to raise 1 g of water by 1 °C.
  • Kilocalorie (kcal) – 1000 calories. In nutrition, this is usually written as “Calorie” with a capital C.

This means that a food label showing “250 Calories” actually means 250 kilocalories, or 250,000 small calories, or 250 × 4184 = 1,046,000 joules.

Common conversions

  • 1 J ≈ 0.0002390057 kcal
  • 1000 J ≈ 0.2390 kcal
  • 1 kcal = 4184 J
  • 2000 kcal (typical daily intake) = 8,368,000 J

FAQ

Is 1 kcal the same as 1 Calorie on food labels?

Yes. In nutrition, “Calorie” (capital C) is defined as 1 kilocalorie (kcal). So 1 Cal = 1 kcal = 1000 cal.

Why do scientists prefer joules?

Joules are part of the SI system, which keeps units consistent across physics, chemistry, and engineering. Kilocalories are still common in nutrition because they give more human‑scale numbers for daily energy intake.

How precise is the conversion 1 kcal = 4184 J?

The value 4184 J per kcal is an exact definition used in modern standards. Older definitions used slightly different values (e.g. 4186.8 J), but 4184 J is now standard.