Ergs to Joules (erg to J)

1 erg equals 1×10⁻⁷ joules exactly.

1 erg = 1×10⁻⁷ joules

How to convert ergs to joules

To convert ergs to joules, multiply the number of ergs by 1×10⁻⁷. This factor is exact. To go the other way, multiply joules by 10,000,000.

joules = ergs × 1×10⁻⁷

Example: 10 ergs = 0.000001 joules.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Erg (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.

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.

1 erg = 1×10⁻⁷ joules (exactly).

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

Joule (J)

Metric (SI)Current unit

The SI unit of energy: the work done by a force of one newton over one meter, or one watt for one second.

James Prescott Joule was born in Salford on 24 December 1818, the son of a wealthy brewer, and later ran the family brewery while treating science as a serious hobby. In June 1845 he told a British Association meeting in Cambridge about his best-known experiment: a falling weight turned a paddle wheel inside an insulated barrel of water, and the water warmed up. Mechanical work turned into heat at a fixed rate, which supported energy conservation and undermined the caloric theory of heat.

The unit came later. On 23 August 1882 Carl Wilhelm Siemens proposed at a British Association meeting that a unit of heat equal to 10 million ergs be named the joule, and in 1889 the second International Electrical Congress adopted it alongside the watt. Joule died that same year. In 1948 the CGPM added that the joule should be preferred to the calorie as the unit of heat, and it entered the SI in 1960.

For scale, one joule is about the energy needed to lift an apple of roughly 102 g by one meter. A 56 g tennis ball moving at 6 m/s carries about one joule of kinetic energy.

The joule is the reference unit for energy on this site.

Sources: Wikipedia: Joule; Wikipedia: James Prescott Joule

Related conversions

See all energy units.