Calories to Joules Converter (cal to J)

Heats of fusion and vaporization, bond energies and calorimeter readings in older chemistry and biology sources are often written in calories or cal/g, while modern SI work and most exam answers expect joules. The calorie is defined from the joule, so the conversion is a single multiplication. Values quoted per gram or per mole convert the same way: multiply the calories by 4.184 and keep the rest of the unit, so cal/g becomes J/g.

Several calories have been defined over the years. This page uses the thermochemical calorie, exactly 4.184 J, common in chemistry; the International Table calorie (4.1868 J) appears mainly in engineering steam tables. If a source does not say which it uses, the difference of about 0.07% rarely matters outside precise thermodynamic work.

How to use this tool

1. Type a value in the Calorie box to see it in joules, or type in the Joule 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

J = cal × 4.184

cal = J ÷ 4.184

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

Example

Two conversions worked with the same factors the converter uses:

540 cal × 4.184 = 2259.36 J

1000 J × 0.239005736138 ≈ 239.006 cal

Calorie to Joule chart

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

Joule to Calorie chart

The reverse direction for values people often look up.

Heat quantities in small calories

Quick mental estimate

Multiply by 4, then add 5% of the result: 540 cal → 2,160 + 108 = 2,268 J. That uses 4.2 J per calorie, about 0.4% above 4.184, so the shortcut runs a little high.

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

The two units

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.

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.