Kilocalories to Kilojoules Converter

Kilocalories to Kilojoules

Convert kilocalories (kcal) to kilojoules (kJ). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.

The Formula

`` kilojoules = kilocalories × 4.184 kilocalories = kilojoules × 0.239005736138 `

One kilocalory is 4.184 kilojoules, and one kilojoule is 0.239006 kilocalories.

Conversion Table

Kilocalories	Kilojoules
1 kcal	4.184 kJ
2 kcal	8.368 kJ
5 kcal	20.92 kJ
10 kcal	41.84 kJ
25 kcal	104.6 kJ
50 kcal	209.2 kJ
100 kcal	418.4 kJ
500 kcal	2,092 kJ
1,000 kcal	4,184 kJ

The Other Direction

Kilojoules	Kilocalories
1 kJ	0.239006 kcal
2 kJ	0.478011 kcal
5 kJ	1.195 kcal
10 kJ	2.3901 kcal
25 kJ	5.9751 kcal
50 kJ	11.9503 kcal
100 kJ	23.9006 kcal
500 kJ	119.5029 kcal
1,000 kJ	239.0057 kcal

What Each Unit Is

Kilocalories (kcal) — 1,000 small calories, or 4,184 joules — the "Calorie" on a nutrition label. Capitalised as Calorie to distinguish it, a convention almost nobody follows.

Kilojoules (kJ) — 1,000 joules. The metric food-energy unit outside North America.

A Sense of Scale

• An apple is 95 kcal
• Daily intake is about 2,000 kcal
• A marathon burns roughly 2,600 kcal
• An apple holds about 400 kJ
• Daily intake is around 8,700 kJ

Doing It in Your Head

Multiply by 21, then divide by 5. That is off by 0.38% — close enough to judge a distance, a weight or a price, and not close enough to sign off on a drawing.

Exact	Mental shortcut
41.84 kJ	42 kJ
418.4 kJ	420 kJ

Precision

The factor 4.184 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.

In Code

`javascript const kilocalorieToKilojoule = (value) => value * 4.184; ``

Where This Conversion Comes Up

• Nutrition
• Electricity
• Fitness
• Heating
• Fuel

How Many Decimals Do You Need?

Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 kcal with the factor truncated at each decimal place:

Decimals kept	Factor	137 kcal becomes	Error
0	4	548	4.3977%
1	4.2	575.4	0.3824%
2	4.18	572.66	0.0956%
3	4.184	573.208	—
4	4.184	573.208	—

A rule that holds for any conversion: round once, at the end. Rounding the factor and then multiplying compounds the error through every subsequent calculation, while carrying full precision and rounding the final answer does not.

The right number of significant figures is set by your input, not by the converter. If you measured kilocalories to three significant figures, the answer in kilojoules is only good to three — writing more digits claims precision the measurement never had.