Convert Electronvolts to Calories

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.

The Calorie (symbol: cal) is a unit of energy. The 'small' gram-calorie (also called thermochemical calorie), defined as exactly 4.184 joules per ISO 31-4 / IUPAC convention — the energy needed to raise one gram of liquid water by 1 °C at standard conditions. This is the scientific calorie used throughout chemistry, physics, and biochemistry literature: enzyme kinetic data, calorimetric measurements (DSC instruments report energy in cal/g for melting transitions), Hess's law calculations, and the thermochemistry tables in the CRC Handbook all use cal. The gram-calorie is NOT the larger 'Calorie' (Cal, capital C) used on US food labels, which is actually a kilocalorie (1 Cal = 1 kcal = 1,000 gram-calories). The cal/Cal naming clash is a notorious source of confusion when cross-referencing nutrition data against scientific literature — a 'low-calorie' food labelled 'only 100 Calories' delivers 100,000 small calories. Two slightly-different historical 'calorie' definitions exist (thermochemical 4.184 J; 'International Table' or IT calorie 4.1868 J), with the thermochemical version dominant in modern usage.

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