Gauss (unit)

The gauss (symbol: G, sometimes Gs) is a unit of measurement of magnetic induction, also known as magnetic flux density. The unit is part of the Gaussian system of units, which inherited it from the older centimetre–gram–second electromagnetic units (CGS-EMU) system. It was named after the German mathematician and physicist Carl Friedrich Gauss in 1936. One gauss is defined as one maxwell per square centimetre.

As the centimetre–gram–second system of units (cgs system) has been superseded by the International System of Units (SI), the use of the gauss has been deprecated by the standards bodies, but is still regularly used in various subfields of science. The SI unit for magnetic flux density is the tesla (symbol T),^[1] which corresponds to 10,000gauss.

Albeit not a component of the International System of Units, the usage of the gauss generally follows the rules for SI units. Since the name is derived from a person's name, its symbol is the uppercase letter "G". When the unit is spelled out, it is written in lowercase ("gauss"), unless it begins a sentence.^{[2]: 147–148} The gauss may be combined with metric prefixes,^[3]: 128 such as in milligauss, mG (or mGs), or kilogauss, kG (or kGs).

$${\displaystyle {\begin{aligned}1\,{\rm {G}}&={\rm {Mx}}{\cdot }{\rm {cm}}^{-2}={\frac {\rm {g}}{{\rm {Bi}}{\cdot }{\rm {s}}^{2}}}\\&{\text{ ≘ }}10^{-4}\,{\rm {T}}=10^{-4}{\frac {\rm {kg}}{{\rm {A}}{\cdot }{\rm {s^{2}}}}}\end{aligned}}}$$

The gauss is the unit of magnetic flux density B in the system of Gaussian units and is equal to Mx/cm² or g/Bi/s², while the oersted is the unit of H-field. One tesla (T) corresponds to 10⁴ gauss, and one ampere (A) per metre corresponds to 4π × 10⁻³ oersted.

The units for magnetic flux Φ, which is the integral of magnetic B-field over an area, are the weber (Wb) in the SI and the maxwell (Mx) in the CGS-Gaussian system. The conversion factor is 10⁸ maxwell per weber, since flux is the integral of field over an area, area having the units of the square of distance, thus 10⁴ G/T (magnetic field conversion factor) times the square of 10² cm/m (linear distance conversion factor). 10⁸ Mx/Wb = 10⁴ G/T × (10² cm/m)².

• 10⁻⁹–10⁻⁸ G – the magnetic field of the human brain
• 10⁻⁶–10⁻³ G – the magnetic field of Galactic molecular clouds. Typical magnetic field strengths within the interstellar medium of the Milky Way are ~5 μG.
• 0.25–0.60 G – the Earth's magnetic field at its surface
• 4 G – near Jupiter's equator
• 25 G – the Earth's magnetic field in its core^[4]
• 50 G – a typical refrigerator magnet
• 100 G – an iron magnet
• 1500 G – within a sun spot^[5]
• 10000 to 13000 G – remanence of a neodymium-iron-boron (NIB) magnet^[6]
• 16000 to 22000 G – saturation of high permeability iron alloys used in transformers^[7]
• 3000–70000 G – a medical magnetic resonance imaging machine
• 10¹²–10¹³ G – the surface of a neutron star^[8]
• 4 × 10¹³ G – the Schwinger limit
• 10¹⁴ G – the magnetic field of SGR J1745-2900, orbiting the supermassive black hole Sgr A* in the center of the Milky Way.
• 10¹⁵ G – the magnetic field of some newly created magnetars^[9]
• 10¹⁷ G – the upper limit to neutron star magnetism^[9]

• Tesla (unit)
• Centimetre–gram–second system of units
• Gaussian units