Calories to Joules Converter

Calories to Joules

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

The Formula

`` joules = calories × 4.184 calories = joules × 0.239005736138 `

One calory is 4.184 joules, and one joule is 0.239006 calories.

Conversion Table

Calories	Joules
1 cal	4.184 J
2 cal	8.368 J
5 cal	20.92 J
10 cal	41.84 J
25 cal	104.6 J
50 cal	209.2 J
100 cal	418.4 J
500 cal	2,092 J
1,000 cal	4,184 J

The Other Direction

Joules	Calories
1 J	0.239006 cal
2 J	0.478011 cal
5 J	1.195 cal
10 J	2.3901 cal
25 J	5.9751 cal
50 J	11.9503 cal
100 J	23.9006 cal
500 J	119.5029 cal
1,000 J	239.0057 cal

What Each Unit Is

Calories (cal) — the energy to raise one gram of water by one degree Celsius, or 4.184 joules — the "small" calorie. A 19th-century thermal unit, displaced by the joule in physics but retained in nutrition.

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.

A Sense of Scale

• A gram of sugar holds about 4,000 small calories
• Lifting an apple one metre takes about 1 J
• A heartbeat uses roughly 1 J

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 J	42 J
418.4 J	420 J

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.

Watch Out For

• Food labels say "calorie" but mean kilocalorie — 1,000 of these. A 200-calorie snack is 200 kcal, or 837 kJ.

In Code

`javascript const calorieToJoule = (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 cal with the factor truncated at each decimal place:

Decimals kept	Factor	137 cal 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 calories to three significant figures, the answer in joules is only good to three — writing more digits claims precision the measurement never had.