What is the difference between a calorie and a kilocalorie?

A small calorie (cal) is the energy needed to raise 1 gram of water by 1 °C. A kilocalorie (kcal) equals 1,000 small calories and is the unit used on food nutrition labels — often written as "Calorie" (capital C) in everyday speech.

What is the exact conversion factor from kcal to kJ?

1 kcal = 4.184 kJ, based on the thermochemical calorie definition. Some older sources use 4.186 kJ (15 °C calorie) — the difference is under 0.05% and negligible for nutrition purposes.

Why do Australian and European food labels show kJ instead of kcal?

The International System of Units (SI) defines the joule as the standard unit of energy. Countries that follow SI closely — including Australia, New Zealand, and most of Europe — mandate kJ on labels, though many also show kcal alongside it.

How many kJ is 2000 kcal?

2000 kcal × 4.184 = 8,368 kJ. The commonly cited daily energy intake of 2,000 Calories (kcal) equals roughly 8,400 kJ.

Is this converter accurate for scientific use?

Yes — the converter uses the thermochemical calorie (1 cal = 4.184 J exactly), which is the definition used in chemistry and nutrition. If you need the 15 °C calorie (4.18580 J) or the IT calorie (4.18674 J), those differ by less than 0.07%.

Calories to Kilojoules Converter

Enter any calorie or kilocalorie value and instantly get the equivalent in kilojoules, with the formula shown.

Input

Input unit

Value (cal)

Result

Enter a value on the left to see the result.

Common energy reference values

Description	kcal	kJ
Medium apple (~180 g)	95 kcal	397 kJ
Slice of white bread	79 kcal	331 kJ
Large egg (boiled)	78 kcal	326 kJ
Cup of whole milk (240 ml)	149 kcal	623 kJ
Daily intake (adult, average)	2,000 kcal	8,368 kJ
1 gram of fat (theoretical)	9 kcal	37.7 kJ

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Summary

This converter handles both small calories (cal, the thermochemical unit) and food kilocalories (kcal, the "Calorie" on nutrition labels) and converts them to kilojoules (kJ). One small calorie equals exactly 4.184 J (0.004184 kJ); one food kilocalorie equals 4.184 kJ because 1 kcal = 1000 cal. All math runs client-side with no server round-trip.

How it works

Select whether your input is in cal (small calories) or kcal (food kilocalories).
Enter the value you want to convert.
The converter multiplies cal × 0.004184 to get kJ, or kcal × 4.184 to get kJ.
The result and full formula update as you type.
Copy the result with one click.

Use cases

Read nutrition labels that show kcal and convert to kJ for Australian or EU packaging.
Cross-check energy values in scientific papers that mix cal and kJ units.
Convert food energy for fitness tracking apps that use kJ.
Translate recipe energy data between US (kcal) and metric (kJ) formats.
Check chemistry homework where thermochemical calories appear.
Compare energy content of foods using a consistent unit.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu