How many electron volts are in 1 GeV?

1 billion

1 billion - 1,000,000,000

In particle physics, the standard unit is the unit of energy GeV. One eV (electron Volt) is the amount of energy that an electron gains when it moves through a potential difference of 1 Volt (in a vacuum). G stands for Giga, or 10^9. Thus a GeV is a billion (in US counting) electron Volts. The mass-energy of a proton or neutron (at rest) is approximately 1 GeV.

A GeV is a billion (in US counting) electron Volts.

An EV unit of energy commonly used in atomic and nuclear physics, equal to the energy gained by an electron (a charged particle carrying unit electronic charge when the electrical potential at the electron increases by one volt). The electron volt equals 1.602 × 10-12 erg. The abbreviation MeV indicates 106 (1,000,000) electron volts and GeV, 109 (1,000,000,000).

http://www2.slac.stanford.edu/vvc/theory/units.html
https://en.wikipedia.org/wiki/Electronvolt
encyclopedia.com/category/Science_and_Technology/Physics/physics.html no longer exists

Just for the record...Prior to the popular usage of the computer term "gigabyte", the prefix was pronounced by the scientific community as it was pronounced in "Back to the Future", jiga.

giga-

- /ji'ga/ or /gi'ga/ pref.

http://dictionary.reference.com/browse/giga