What Is a Tesla (Unit)?
The tesla (T) is the SI unit of magnetic flux density. Here is what it measures, how it relates to the gauss, and how strong common magnetic fields really are.
Last updated: 2026-05-21
Definition
The tesla (symbol T) is the SI derived unit of magnetic flux density, also called magnetic field strength or B-field. It quantifies how concentrated a magnetic field is at a given point in space.
One tesla equals one weber of magnetic flux distributed evenly over one square meter of area:
1 T = 1 Wb/m²
Expressed in SI base units, the tesla resolves to kilograms per ampere per second squared: 1 T = 1 kg/(A·s²). Equivalently, it can be written as one volt-second per square meter (V·s/m²) or one newton per ampere-meter (N/(A·m)). Each form describes the same physical quantity from a different starting point — flux, force, or induced voltage.
Tesla vs Gauss
Before the tesla was adopted, magnetic flux density was measured in the gauss (G), the unit from the older centimeter-gram-second (CGS) system. The two relate by a fixed factor:
1 T = 10,000 G and 1 G = 100 µT
The tesla is the modern SI standard and is preferred in engineering, medicine, and most scientific publishing. The gauss survives in physics labs, electronics, and consumer magnet specifications, where field values are small and the gauss gives more convenient numbers — a fridge magnet reads more naturally as 50 G than as 0.005 T. You can move between both units instantly with the magnetic flux density converter.
Everyday Examples
Magnetic fields span an enormous range. The table below lists familiar reference points from the faint field of the human body to the extreme fields of dead stars.
| Source | Approximate flux density |
|---|---|
| Human brain activity | ~1 femtotesla (10−15 T) |
| Earth's surface field | 25–65 µT |
| Refrigerator magnet | ~5 mT |
| Sunspot | ~0.1–0.4 T |
| Clinical MRI scanner | 1.5–3 T |
| Strongest continuous lab magnets | ~45 T |
| Strongest pulsed lab magnets | ~1,200 T (microseconds) |
| Neutron star surface | ~10⁸–10¹¹ T |
| Magnetar (extreme neutron star) | up to ~10¹¹ T |
Common Sub-multiples and Multiples
Because most practical fields are far weaker than one tesla, sub-multiples are used constantly. The gauss is included for reference since it remains in wide use.
| Unit | Symbol | Value in tesla |
|---|---|---|
| Tesla | T | 1 T |
| Millitesla | mT | 0.001 T (10−3 T) |
| Microtesla | µT | 0.000001 T (10−6 T) |
| Nanotesla | nT | 10−9 T |
| Gauss | G | 0.0001 T (10−4 T) |
History
The unit is named after Nikola Tesla (1856–1943), the Serbian-American inventor and electrical engineer whose work on alternating current, induction motors, and rotating magnetic fields shaped modern power systems. The name was formally adopted by the General Conference on Weights and Measures in 1960, replacing the older practice of measuring flux density in gauss within the SI framework.
The tesla joins the weber (magnetic flux) and the henry (inductance) as part of the coherent set of SI units describing electromagnetism. Note that the unit and the carmaker Tesla, Inc. are not connected — the company, founded in 2003, simply shares the same namesake honoring Nikola Tesla.
To switch between tesla, gauss, millitesla, and microtesla without doing the arithmetic by hand, use the magnetic flux density converter for fast, precise results.