Gigaelectron-volts (GeV) to electron-volts (eV): 1 GeV = 109eV
In physics, the electron volt (symbol eV; also written electronvolt) is a unit of energy equal to approximately 1.6×10-19 joule (symbol J). By definition, it is the amount of energy gained (or lost) by the charge of a single electron moved across an electric potential difference of one volt. Thus it is 1 volt (1 joule per coulomb, 1 J/C) multiplied by the elementary charge (e, or 1.602176565(35)×10-19 C). Therefore, one electron volt is equal to 1.602176565(35)×10-19 J. Historically, the electron volt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with charge q has an energy E = qV after passing through the potential V; if q is quoted in integer units of the elementary charge and the terminal bias in volts, one gets an energy in eV.