Joules to Kilocalories Converter

Joules to Kilocalories

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

The Formula

`` kilocalories = joules × 0.000239005736138 joules = kilocalories × 4184 `

One joule is 2.3901e-4 kilocalories, and one kilocalory is 4,184 joules.

Conversion Table

Joules	Kilocalories
1 J	2.3901e-4 kcal
2 J	4.7801e-4 kcal
5 J	0.001195 kcal
10 J	0.00239 kcal
25 J	0.005975 kcal
50 J	0.01195 kcal
100 J	0.023901 kcal
500 J	0.119503 kcal
1,000 J	0.239006 kcal

The Other Direction

Kilocalories	Joules
1 kcal	4,184 J
2 kcal	8,368 J
5 kcal	20,920 J
10 kcal	41,840 J
25 kcal	104,600 J
50 kcal	209,200 J
100 kcal	418,400 J
500 kcal	2,092,000 J
1,000 kcal	4,184,000 J

What Each Unit Is

Joules (J) — the work done by one newton acting over one metre — the SI derived unit of energy. Named for James Prescott Joule, who established the mechanical equivalent of heat.

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.

A Sense of Scale

• Lifting an apple one metre takes about 1 J
• A heartbeat uses roughly 1 J
• An apple is 95 kcal
• Daily intake is about 2,000 kcal
• A marathon burns roughly 2,600 kcal

Precision

The factor 0.000239005736138 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 jouleToKilocalorie = (value) => value * 0.000239005736138; ``

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 J with the factor truncated at each decimal place:

Decimals kept	Factor	137 J becomes	Error
0	0	0	100.0000%
1	0	0	100.0000%
2	0	0	100.0000%
3	0	0	100.0000%
4	0.0002	0.0274	16.3200%

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 joules to three significant figures, the answer in kilocalories is only good to three — writing more digits claims precision the measurement never had.