Joules to Calories Converter (J to cal)

Physics problems, SI data tables and lab instruments give energy in joules, while older chemistry textbooks, calorimetry results and some reference tables still use the small calorie. One joule is the work of a one-newton force acting over one meter; one calorie was originally the heat that warms a gram of water by one degree Celsius. The calorie is neither an SI unit nor one accepted for use with the SI, so journals and exam boards generally expect energy in joules.

Because that heat depends slightly on the water's starting temperature, the calorie was later fixed in joules. This converter uses the thermochemical calorie, exactly 4.184 J; the International Table calorie found in some steam tables is 4.1868 J, about 0.07% larger, so check which one a source means when the fourth digit matters.

How to use this tool

1. Type a value in the Joule box to see it in calories, or type in the Calorie box to convert the other way.
2. Press ⇄ to swap the two units, or Load example for a typical value.
3. Check the charts below for common values; for other units, open the Energy converter.

Formula

cal = J ÷ 4.184

J = cal × 4.184

Both factors come from exact definitions: 1 calorie = 4.184 joules and 1 joule = 0.239005736138 calories (shown to 12 significant digits).

Example

Two conversions worked with the same factors the converter uses:

1000 J × 0.239005736138 ≈ 239.006 cal

80 cal × 4.184 = 334.72 J

Joule to Calorie chart

Common values from joules to calories, rounded to four decimal places.

Calorie to Joule chart

The reverse direction for values people often look up.

Amounts of energy in joules

Quick mental estimate

Divide by 4, then take away 4% of the answer: 1,000 J → 250 − 10 = 240 cal. That equals dividing by about 4.17, so the result comes out roughly 0.4% high.

Use the converter or the charts when the exact figure matters.

The two units

Joule (J): The joule (J) is the SI unit of energy. One joule is the work of a constant one-newton force over one metre of displacement in the force direction, or the energy transferred by one watt in one second.

Calorie (cal): This converter uses the thermochemical calorie, defined as exactly 4.184 J, roughly the energy needed to warm one gram of water by 1 °C. The International Table calorie (4.1868 J) is about 0.07% larger.