Erg

CGS & old metricTraditional unit (still used in some regions)

Exactly 10⁻⁷ joules. The energy unit of the old centimeter-gram-second (CGS) system, still used in astrophysics.

1 erg = 1×10⁻⁷ joules (exactly).

1 erg = 1×10⁻⁷ joules

About the erg

Erg takes its name from the Greek ergon, meaning work. Rudolf Clausius proposed that word for a unit of energy in 1864, and in 1873 a British Association committee including Maxwell and Thomson asked that erg be reserved for the energy unit of the centimeter-gram-second system.

It is the work done by a force of one dyne acting through one centimeter, or 1 g cm2/s2. That equals 10 to the power minus 7 joule, 100 nanojoules, which is a very small amount of energy and was a natural size for laboratory experiments of the era.

The erg is not an SI unit, and NIST lists it only as a conversion factor to the joule. It survives mainly in astrophysics and theoretical physics, where Gaussian CGS units remain common, so cosmic energies are still often given in ergs.

Sources: Wikipedia: Erg (unit); Wikipedia: Centimetre-gram-second system of units; NIST SP 811, Appendix B.8 conversion factors

Erg conversion chart

1 erg expressed in every other energy unit:

Unit1 erg
Joules1×10⁻⁷
Kilojoules1×10⁻¹⁰
Watt-hours2.777777778×10⁻¹¹
Kilowatt-hours2.777777778×10⁻¹⁴
British Thermal Units9.478171203×10⁻¹¹
Calories2.390057361×10⁻⁸
Kilocalories2.390057361×10⁻¹¹
Megajoules1×10⁻¹³
Gigajoules1×10⁻¹⁶
Megawatt-hours2.777777778×10⁻¹⁷
Foot-pounds7.375621493×10⁻⁸
Millijoules0.0001
Electronvolts624,150,907,446
Kiloelectronvolts624,150,907.4
Megaelectronvolts624,150.9074
Gigaelectronvolts624.1509074
Tons Of TNT2.390057361×10⁻¹⁷
Tonnes Of Oil Equivalent2.388458966×10⁻¹⁸
Therms9.48043428×10⁻¹⁶
Quads9.478171203×10⁻²⁶
Calories (IT)2.388458966×10⁻⁸
Kilogram-force Meters1.019716213×10⁻⁸
Horsepower-hours3.72506136×10⁻¹⁴
Liter-atmospheres9.869232667×10⁻¹⁰

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