Convert Kilocalories to Electronvolts

The Kilocalorie (symbol: kcal) is a unit of energy. A unit of energy equal to exactly 1,000 gram-calories (= exactly 4,184 joules per the thermochemical definition). This is the unit behind the 'Calorie' (capital C) on US food packaging — a 200-Calorie granola bar contains 200 kcal = 200,000 small calories = 836 kJ. Adult daily dietary intake per FDA / USDA Dietary Guidelines is 1,600-2,400 kcal for women and 2,000-3,000 kcal for men depending on age and activity, with WHO baseline targets of 2,000 / 2,500 kcal. Indirect calorimetry (gold-standard metabolic rate measurement) reports BMR / TDEE in kcal/day. Kilocalories are also used for refrigeration / heating-system output in some legacy European industrial specifications (kcal/h sometimes appears on older boilers and chillers, though kW has largely replaced it), and for muscle-physiology energy-expenditure reporting in exercise science. The 'Atwater system' (4-9-4 macronutrient values: 4 kcal/g protein, 9 kcal/g fat, 4 kcal/g carbohydrate) is the calculation method behind almost every nutrition label.

Kilocalories are commonly used in nutrition, electrical billing, physics, and mechanical engineering.

The Electronvolt (symbol: eV) is a unit of energy. A unit of energy equal to the kinetic energy gained by an electron accelerating through an electric potential difference of one volt in vacuum, defined since the 2019 SI redefinition as exactly 1.602176634 × 10⁻¹⁹ joules (CODATA 2018, BIPM SI Brochure). The electronvolt is the natural working unit of atomic, molecular, and particle physics where joules are too large to be convenient: chemical bond energies are a few eV (C-C bond ~3.6 eV, O-H bond ~4.8 eV), photon energies in the visible spectrum are 1.6-3.1 eV (red to violet), X-rays carry keV (medical diagnostic ~80-140 keV, hard X-ray ~10-100 keV), nuclear-reaction Q-values are MeV (fission of U-235 releases ~200 MeV per atom), particle-collider beam energies are GeV-TeV (LHC operates at 13.6 TeV center-of-mass), and astrophysical sources reach PeV / EeV (highest-energy cosmic rays ~3 × 10²⁰ eV = 300 EeV). Particle physics papers in Physical Review D, JHEP, Nature Physics, and the PDG Review of Particle Physics report all energies, masses (E = mc² gives a free conversion), and cross-sections in eV or its derivatives. 1 eV ≈ 1.602 × 10⁻¹⁹ J ≈ 1.602 × 10⁻¹² erg.

Electronvolts are commonly used in nutrition, electrical billing, physics, and mechanical engineering.