In the centimeter-gram-second electromagnetic system of units, the unit of magnetic field strength. Symbol, Oe.

In a vacuum, the value of the magnetic intensity in oersteds at a point is equal to the force in dynes exerted on a unit magnetic pole placed at the point.

Later the oersted was redefined as the strength of the magnetic field at a distance of 1 centimeter from a straight conductor of infinite length and negligible circular cross section which carries a current of 0.5 abamperes. One oersted corresponds to approximately 79.577 47 amperes per meter; real equivalence between a unit in a 3-dimensional cgs system and one in the 4-dimensional SI is not possible.

In 1927, the IEC set up a subcommittee to unravel the conflicting uses of the term gauss. The subcommittee decided that flux density (conventionally, B) and magnetizing force (H) should have different units. Flux density would be measured in gauss, and a new unit of magnetic field strength, to be called the oersted, would be added to the cgs system. The committee’s recommendation was adopted by the IEC plenary convention at Oslo in 1930, and subsequently endorsed by the IUPAP.

engraving of Oersted

Hans Christian Ørsted

The oersted is named for Hans Christian Ørsted (1777 – 1851), the Danish physicist who first observed the magnetism of a wire carrying an electric current.

According to the current national standard in the United States¹, the oersted is not to be used. Amperes per meter should be used instead.

1. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.

See Section 3.3.3.

I.E.C. report on meetings held at Bellagio, Italy, Advisory Committee No. 1, 1927.

Resume of plenary meeting of IEC in Scandinavia, 1930. Magnetic Units, document R.M. 77.

International Electrotechnical Commission.
Recommendations in the field of quantities and units used in electricity. (1st ed.)
IEC Publication 164.
Geneva, 1964.

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