Convert kilo-electronvolt to joule

The calorie of food labels is really the kilocalorie: 1 kcal = 1,000 cal = 4.1868 kJ, the heat that warms a kilogram of water by one degree. Nutrition labels in the EU must give both kJ and kcal, the US gives 'Calories' with a capital C meaning kcal, and the adult reference intake is 2,000 kcal, about 8,400 kJ. A slice of bread is around 80 kcal, an hour's brisk walk burns about 300.

The electronvolt is the energy an electron gains crossing one volt, 1.602 × 10⁻¹⁹ J, and is the natural unit of the very small. Chemical bonds and visible light are a few eV, X-rays tens of keV, nuclear gamma rays MeV, and the Large Hadron Collider brings protons to 6.8 TeV each. Through E = mc² it also serves as a mass unit: an electron is 0.511 MeV, a proton 938 MeV, and the Higgs boson 125 GeV.