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To convert thermochemical calories to joules, multiply by 4.184. So 1 cal = 4.184 J, 100 cal = 418.4 J, and 1,000 cal = 4,184 J (= 1 kcal). Remember: food packaging "Calories" (capital C) are kilocalories — 1 food Calorie = 4,184 J.
The joule is the SI unit for all forms of energy — heat, mechanical work, and electrical energy. Converting calories to joules allows comparison across different energy types. A 2,000-kcal daily diet is 8,368,000 J (8.37 MJ) — enough energy to lift a 1,000 kg car 855 meters off the ground.
Did you know? James Prescott Joule (1818–1889) demonstrated through careful experiments that mechanical work and heat are both forms of energy, establishing the mechanical equivalent of heat as 4.15–4.19 J/cal. His work laid the foundation for the law of conservation of energy.
Physics homework requiring SI units for energy equations. Comparing food energy (kcal) with electrical energy (J, kWh) to understand energy scale. Lab reports on reaction enthalpies measured in calories that must be expressed in joules for publication in international journals.