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Tesla (unit)

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The tesla (symbol: T) is the unit of magnetic flux density (B) (also called magnetic B-field) in the International System of Units (SI).

tesla
Unit systemSI
Unit ofmagnetic flux density
SymbolT
Named afterNikola Tesla
In SI base units
1 T= 1 kg⋅s−2⋅A−1
In Gaussian units
1 Tcorresponds to[1] 104 G

One tesla is equal to one weber per square metre. The unit was announced during the General Conference on Weights and Measures in 1960 and is named[2] in honour of Serbian-American electrical and mechanical engineer Nikola Tesla, upon the proposal of the Slovenian electrical engineer France Avčin. As with every SI unit named after a person, its symbol is upper case (T) but the name of the unit is written in sentence case (tesla).

Definition

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Statue of Nikola Tesla outside the National Library of Serbia; inscribed on the plaque is the formula

A particle, carrying a charge of one coulomb (C), and moving perpendicularly through a magnetic field of one tesla, at a speed of one metre per second (m/s), experiences a force with magnitude one newton (N), according to the Lorentz force law. That is, Expressed in SI base units, 1 tesla is: where A is ampere, kg is kilogram, and s is second.[3]

In terms of other SI derived units

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As an SI derived unit, the tesla can also be expressed in terms of other units. For example, a magnetic flux of 1 weber (Wb) through a surface of one square meter is equal to a magnetic flux density of 1 tesla.[3] That is,

Additional equivalences result from the derivation of coulombs from amperes (A), : the relationship between newtons and joules (J), : and the derivation of the weber from volts (V), :

Conversion to non-SI units

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The CGS system has a unit similar to the tesla called the gauss. One tesla corresponds to 104 G, but there are subtle differences in the meaning of the units and the gauss is not acceptable for use with SI units according to NIST guidelines.[1]

The unit γ (gamma), formerly used in geophysics and defined as 10-5 G, corresponds to 10-9 T. The modern convention is to use the nanotesla (nT) instead of γ.[4][5]

The 2019 revision of the SI changed the definition of the ampere[6] and that changed the definition of the tesla by 106.67 parts in 109.[7] The revision also changed the definition of the permeability constant, , altering the meaning of conversions between SI units like the tesla and CGS units like the gauss, and making them a little uncertain. Use of these conversions has been discouraged in scholarly journals.[8]

Examples

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Map of the intensity of Earth's magnetic field, using conventional units of nanoTesla, nT

The following examples are listed in the ascending order of the magnetic-field strength.

  • 25000–65000 nT – the magnitude of Earth's magnetic field at its surface[9]
  • 4×10−5 T (40 μT) – walking under a high-voltage power line[10]
  • 5×10−3 T (5 mT) – the strength of a typical refrigerator magnet
  • 0.3 T – the strength of solar sunspots
  • 1 T to 2.4 T – coil gap of a typical loudspeaker magnet
  • 1.5 T to 3 T – strength of medical magnetic resonance imaging systems in practice, experimentally up to 17 T[11]
  • 4 T – strength of the superconducting magnet built around the CMS detector at CERN[12]
  • 5.16 T – the strength of a specially designed room temperature Halbach array[13]
  • 8 T – the strength of LHC magnets
  • 11.75 T – the strength of INUMAC magnets, largest MRI scanner[14]
  • 13 T – strength of the superconducting ITER magnet system[15]
  • 14.5 T – highest magnetic field strength ever recorded for an accelerator steering magnet at Fermilab[16]
  • 16 T – magnetic field strength required to levitate a frog[17] (by diamagnetic levitation of the water in its body tissues) according to the 2000 Ig Nobel Prize in Physics[18]
  • 17.6 T – strongest field trapped in a superconductor in a lab as of July 2014[19]
  • 20 T – strength of the large scale high temperature superconducting magnet developed by MIT and Commonwealth Fusion Systems to be used in fusion reactors[20]
  • 27 T – maximal field strengths of superconducting electromagnets at cryogenic temperatures
  • 35.4 T – the current (2009) world record for a superconducting electromagnet in a background magnetic field[21]
  • 45 T – the current (2015) world record for continuous field magnets[21]
  • 97.4 T – strongest magnetic field produced by a "non-destructive" magnet[22]
  • 100 T – approximate magnetic field strength of a typical white dwarf star
  • 1200 T – the field, lasting for about 100 microseconds, formed using the electromagnetic flux-compression technique[23]
  • 109 T – Schwinger limit above which the electromagnetic field itself is expected to become nonlinear
  • 108 – 1011 T (100 MT – 100 GT) – magnetic strength range of magnetar neutron stars

Notes and references

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  1. 1 2 "NIST Guide to the SI, Chapter 5: Units Outside the SI". NIST. January 28, 2016.
  2. ↑ "Details of SI units". sizes.com. 2011-07-01. Retrieved 2011-10-04.
  3. 1 2 The International System of Units (PDF), V3.01 (9th ed.), International Bureau of Weights and Measures, Aug 2024, ISBN 978-92-822-2272-0
  4. ↑ A Dictionary of Earth Sciences (3 ed.). Oxford University Press. January 1, 2008. doi:10.1093/acref/9780199211944.001.0001. ISBN 978-0-19-921194-4."gamma". www.oxfordreference.com. Oxford, UK: Oxford University Press. Retrieved 2026-06-07.
  5. ↑ McGraw Hill Encyclopaedia of Physics (2nd edition), C. B. Parker, 1994, ISBN 0-07-051400-3.[page needed]
  6. ↑ "SI base unit: ampere (A)". www.bipm.org. Sevres, France: Bureau International des Poids et Mesures. 2019. Retrieved 2026-06-07."Historical perspective: Unit of electric current, ampere". www.bipm.org. Sevres, France: Bureau International des Poids et Mesures. 2019. Retrieved 2026-06-07.
  7. ↑ Shisong Li; Qing Wang; Wei Zhao; Songling Huang (2020-07-20). "From μ0 to e: A Survey of Major Impacts for Electrical Measurements in Recent SI Revision". ieeexplore.ieee.org. IEEE. Retrieved 2026-06-10.
  8. ↑ "Ronald B. Goldfarb" (2017). "The Permeability of Vacuum and the Revised International System of Units". ieeexplore.ieee.org. IEEE. Retrieved 2026-06-10.
  9. ↑ Finlay, C. C.; Maus, S.; Beggan, C. D.; Bondar, T. N.; Chambodut, A.; Chernova, T. A.; Chulliat, A.; Golovkov, V. P.; Hamilton, B.; Hamoudi, M.; Holme, R.; Hulot, G.; Kuang, W.; Langlais, B.; Lesur, V.; Lowes, F. J.; Lühr, H.; Macmillan, S.; Mandea, M.; McLean, S.; Manoj, C.; Menvielle, M.; Michaelis, I.; Olsen, N.; Rauberg, J.; Rother, M.; Sabaka, T. J.; Tangborn, A.; Tøffner-Clausen, L.; Thébault, E.; Thomson, A. W. P.; Wardinski, I.; Wei, Z.; Zvereva, T. I. (December 2010). "International Geomagnetic Reference Field: the eleventh generation". Geophysical Journal International. 183 (3): 1216–1230. Bibcode:2010GeoJI.183.1216F. doi:10.1111/j.1365-246X.2010.04804.x. hdl:20.500.11850/27303.
  10. ↑ "EMF: 7. Extremely low frequency fields like those from power lines and household appliances". ec.europa.eu. Archived from the original on 2021-02-24. Retrieved 2022-05-13.
  11. ↑ "Ultra-High Field". Bruker BioSpin. Retrieved 4 October 2011.{{cite web}}: CS1 maint: deprecated archival service (link)
  12. ↑ "Superconducting Magnet in CMS". Retrieved 9 February 2013.
  13. ↑ "The Strongest Permanent Dipole Magnet" (PDF). Retrieved 2 May 2020.
  14. ↑ "ISEULT – INUMAC". Retrieved 17 February 2014.
  15. ↑ "ITER – the way to new energy". Retrieved 19 April 2012.
  16. ↑ Hesla, Leah (13 July 2020). "Fermilab achieves 14.5-tesla field for accelerator magnet, setting new world record". Retrieved 13 July 2020.
  17. ↑ Berry, M. V.; Geim, A. K. (1997). "Of Flying Frogs and Levitrons" by M. V. Berry and A. K. Geim, European Journal of Physics, v. 18, 1997, p. 307–13" (PDF). European Journal of Physics. 18 (4): 307–313. doi:10.1088/0143-0807/18/4/012. S2CID 1499061. Archived from the original (PDF) on 8 October 2020. Retrieved 4 October 2020.
  18. ↑ "The 2000 Ig Nobel Prize Winners". August 2006. Retrieved 12 May 2013.)
  19. ↑ "Superconductor Traps The Strongest Magnetic Field Yet". 2 July 2014. Retrieved 2 July 2014.
  20. ↑ Hartwig, Zachary S. (March 2024). "The SPARC Toroidal Field Model Coil Program". IEEE Transactions on Applied Superconductivity. 34 (2): 1–16. doi:10.1109/TASC.2023.3332613. ISSN 1051-8223.
  21. 1 2 "Mag Lab World Records". Media Center. National High Magnetic Field Laboratory, USA. 2008. Retrieved 24 October 2015.
  22. ↑ "World record pulsed magnetic field". Physics World. 31 August 2011. Retrieved 26 January 2022.)
  23. ↑ D. Nakamura, A. Ikeda, H. Sawabe, Y. H. Matsuda, and S. Takeyama (2018), Magnetic field milestone
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