Tesla (SI unit)

Last revised by Daniel J Bell on 17 Jun 2021

The tesla (symbol T) is the derived SI unit of magnetic flux density, which represents the strength of a magnetic field. One tesla represents one weber per square meter. The equivalent, and superseded, cgs unit is the gauss (G); one tesla equals exactly 10,000 gauss.

Most current medical magnetic resonance imaging (MRI) units utilize 1.5 T or 3 T field strengths. Open MRI (with an open-side architecture and vertically oriented field) operate at up to 1.2 T. Ultra-high field MRI at 7 T have recently been approved for clinical use in humans, while even higher field strengths up to 17 T are used for preclinical studies in smaller animals.

In comparison, the strength of the earth's magnetic field strength is 24-64 µT 1, five orders of magnitude weaker than the magnets used for MRI.


As for all eponymous SI units when the unit is written out in full it is not capitalized, but when shortened to its symbol it is capitalized.

It is important to emphasize that in common with standard scientific unit notation, a space must always be inserted between the quantity and the unit symbol, therefore 1.5 T and 3 T are correct, conversely 1.5T and 3T are incorrect, despite the latter usages often being seen in medical media and some radiology reports.

History and etymology

It is named after Nikola Tesla (1856-1943) 2, a Croatian-American physicist, inventor and electrical engineer.

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