An erg (short for ergon, a Greek word meaning "work") is a unit of energy and mechanical work equal to 10−7 joules. It originated in the centimetre–gram–second (CGS) system of units, symbol "erg". It is not an SI unit.
An erg is the amount of work done by a force of one dyne exerted for a distance of one centimeter. In the CGS base units, it is equal to one gram centimeter-squared per second-squared (g·cm2/s2). It is thus equal to 10−7 joules or 100 nanojoules (nJ) in SI units.
1 erg = 10−10sn·m = 100 psn·m = 100 picosthène-metres
1 erg = 624.15 GeV = 6.2415×1011 eV
1 erg = 1 dyne cm = 1 g·cm2/s2