Convert Calorie to Joule (cal → J)

Converting calories to joules is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in calories

   Start with the number of calories (cal) you want to convert.
2. 2
   Multiply by 4.184

   The conversion factor from cal to J is 4.184. Multiply your value by this number.
3. 3
   Read the result in joules

   The result is your value in joules (J).

Multiply the value in calories by 4.184. For the reverse direction, multiply by 0.239006.

• ✓1 cal = 4.184 J. 1 kcal = 4184 J.
• ✓Scientific "calorie" and nutrition "Calorie" differ by 1000×.
• ✓Prefer joules in modern scientific writing.

• ✗Assuming "calories" on food labels means gram calories — they are kcal.
• ✗Mixing gram calories and kilocalories in calculations.
• ✗Confusing calorie (energy) with calorimeter (apparatus).

What is the Calorie?

The calorie equals exactly 4.184 joules (the 'thermochemical calorie') and is the historical unit for heat in chemistry and physics. It was originally defined as the heat needed to raise 1 gram of water by 1°C (a definition that varied slightly with starting temperature, hence multiple 'calories' — 4.184 J was set as the exact thermochemical convention). The calorie is widely used in older physics and chemistry literature for reaction energies, specific heat capacities, and thermodynamic calculations. Note: this 'small calorie' (lowercase c) is 1/1000 of the food Calorie (capital C) used in nutrition. The chemistry calorie relates to the joule (4.184 J = 1 cal), the kilocalorie (1,000 cal = 1 kcal = 1 food Calorie), and the BTU (1 BTU ≈ 252 cal). Modern SI usage in scientific publications has largely replaced the calorie with the joule, but it persists in medical and chemistry contexts.

• Thermodynamics and older physics texts
• Chemistry energy calculations
• Some engineering heat-transfer contexts

What is the Joule?

The joule is the SI unit of energy, work, and heat, named after English physicist James Prescott Joule (1818–1889). Defined as the energy transferred when a force of one newton acts over a distance of one meter (1 J = 1 N·m), the joule unifies mechanical work, electrical energy (1 J = 1 watt-second = 1 V·C), and thermal energy. A typical apple has about 250,000 joules of chemical energy when metabolized, lifting an apple 1 meter requires roughly 1 joule of mechanical work, and a single joule could light a 1-watt LED for one second. The joule is fundamental in physics, mechanical engineering, electrical engineering, and nutrition (European food labels show kilojoules). It relates to the kilojoule (1 kJ = 1,000 J), the calorie (1 cal = 4.184 J), the watt-hour (1 Wh = 3,600 J), and the BTU (1 BTU ≈ 1,055 J). Modern definitions of the kilogram and the Kelvin both reference the joule.

• Physics and engineering calculations
• Scientific nutrition measurement (European labels)
• Impact energy in engineering (Charpy test)