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Calorie (thermochemical) (cal)

Quantity: energy · Category: Energy

The thermochemical calorie is a unit of energy defined as exactly 4.184 joules. Historically the calorie was the energy needed to warm one gram of water by one degree Celsius, but several slightly different definitions existed; the thermochemical calorie is now fixed by convention. Distinguish it from the food Calorie (capital C), which is one kilocalorie — 1000 small calories.

Relation to SI

1 cal = 4.184 J exactly (thermochemical)

Examples

  • Food energy: 1 food Calorie = 1 kcal = 1000 cal = 4184 J
  • Specific heat of water ≈ 1 cal/(g·°C) = 4.184 J/(g·°C)
  • Calorimetry often measures heat in calories before converting to joules