Calorie to Kilojoule Converter (cal to kJ)

1 calorie equals 0.004184 kilojoules (kJ) — multiply the number of calories by 0.004184 to convert. This follows from the thermochemical calorie of 4.184 joules, divided by 1,000 to reach kilojoules.

The formula

Multiply calories by the exact factor 0.004184:

kJ = cal × 0.004184

For example, 1000 cal × 0.004184 = 4.184 kJ. To reverse it, divide by 0.004184 (or multiply by 239.005736).

Conversion table

How to convert online

1. Type the number of calories into the first box.
2. Read the kilojoule result instantly in the second box.
3. Enter a kJ value instead to convert back to calories — it works both ways.

Use the Calorie to Kilojoule Converter — free and instant in your browser.

Where this conversion is used

Many countries print food energy in kilojoules, while calories dominate elsewhere and in older references. Converting cal to kJ is handy for reading international nutrition labels, comparing energy figures across standards, and expressing heat values in the SI-based kilojoule.

Scaling and accuracy

The conversion is linear, so results scale cleanly: since 100 cal = 0.4184 kJ, then 250 cal = 1.046 kJ and 1,000 cal = 4.184 kJ. For nutrition, the useful shortcut is that one food Calorie (kcal) equals 4.184 kJ, so a 500 Calorie meal is about 2,092 kJ. This tool uses the thermochemical calorie of exactly 4.184 J; the steam-table calorie of 4.1868 J differs by under 0.1%, which almost never affects everyday figures but is worth noting for precise scientific work where the calorie definition is specified.

FAQ

How many kilojoules are in a calorie?

One calorie equals 0.004184 kJ. Multiply calories by 0.004184 — for example, 10 cal = 0.04184 kJ.

How many kilojoules are in a food Calorie?

A food Calorie (kcal) is 1,000 small calories, so it equals 4.184 kJ.

How do I convert kilojoules back to calories?

Divide by 0.004184, or multiply by 239.005736. For instance, 1 kJ ≈ 239 cal.

Is the conversion exact?

Yes. 0.004184 is exact because the thermochemical calorie is defined as exactly 4.184 J.

Related converters

• Kilojoule to Calorie Converter
• Calorie to Joule Converter
• Calorie to Kilocalorie Converter
• Calorie to Watt-hour Converter

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