Magnetic Flux Density Converter: Tesla, Gauss, mT, µT
Magnetic flux density (the B-field) measures how concentrated a magnetic field is in a given area. The SI unit is the tesla (T), defined as one weber per square metre. In everyday life the fields you encounter are far smaller: Earth's magnetic field runs from about 25 microtesla near the equator to 65 microtesla near the poles, a refrigerator magnet produces roughly 5 millitesla, and a clinical MRI scanner operates at 1.5 to 3 tesla. Outside the SI system, the gauss (G) from the older CGS system remains common in geophysics and materials science, where 1 G equals exactly 10^-4 T. The oersted (Oe) is technically a unit of magnetic field strength (H-field), but in vacuum the numerical value of B in gauss equals H in oersteds, so it is included here as a vacuum-equivalent conversion. Type a value into any field below and all eight units update instantly.
Note: the oersted (Oe) is listed as the vacuum equivalent of B-field only (1 Oe = 10^-4 T in free space). In magnetic materials the relationship differs.
Magnetic flux density conversion factors
All units are expressed relative to the tesla (T). The gauss is the CGS unit; the oersted figure applies in vacuum only.
| Unit | Symbol | Equivalent in Tesla (T) |
|---|---|---|
| Tesla | T | 1 |
| Millitesla | mT | 0.001 |
| Microtesla | µT | 0.000001 |
| Nanotesla | nT | 0.000000001 |
| Gauss | G | 0.0001 |
| Milligauss | mG | 0.0000001 |
| Kilogauss | kG | 0.1 |
| Oersted (vacuum equiv.) | Oe | 0.0001 |
Reference field strengths
| Source | Approximate field strength |
|---|---|
| Earth's magnetic field | 25 to 65 µT (0.25 to 0.65 G) |
| Power line at ground level | 0.1 to 1 µT |
| Refrigerator magnet | ~5 mT (50 G) |
| Loudspeaker magnet | ~1 T (10 kG) |
| Clinical MRI scanner | 1.5 to 3 T |
| Research MRI scanner | 7 to 21 T |
| Neodymium permanent magnet (surface) | up to ~1.4 T |
| Superconducting magnet (record) | up to ~45 T |
Frequently asked questions
What is magnetic flux density and how does it differ from magnetic field strength?
Magnetic flux density (B) measures the concentration of magnetic field lines per unit area and is expressed in tesla (T) in the SI system. Magnetic field strength (H) is a separate quantity measured in amperes per metre (A/m) and relates to the source of the magnetic field, not the medium. In free space (vacuum), B and H are related by the permeability of free space: B = µ0 * H. The two quantities are numerically equal in CGS units, which can cause confusion, but they are physically distinct.
What is a tesla and how was it defined?
The tesla (T) is the SI unit of magnetic flux density, named after inventor Nikola Tesla and adopted by the CGPM in 1960. One tesla equals one weber per square metre (1 T = 1 Wb/m²). It is also equal to one kilogram per ampere per second squared (1 T = 1 kg/(A·s²)). A tesla is a relatively strong field: Earth's field is around 25 to 65 microtesla, while clinical MRI scanners operate at 1.5 to 3 T.
What is the Gauss unit and what is it used for?
The gauss (G) is a CGS unit of magnetic flux density equal to exactly 10^-4 tesla. It predates the SI system and remains in use in some areas of geophysics, materials science, and older technical literature. Earth's magnetic field is approximately 0.25 to 0.65 gauss (25 to 65 microtesla). Most modern scientific and engineering work uses SI units (tesla and its multiples), but gauss still appears in sensor datasheets and industrial magnetics.
What magnetic field strength is used in MRI machines?
Clinical MRI scanners operate at 1.5 T or 3 T, which is roughly 30,000 to 60,000 times Earth's magnetic field. Research MRI systems reach 7 T to 21 T for human studies, and experimental magnets have reached world records above 45 T. Higher field strengths improve image resolution and signal-to-noise ratio but require more powerful and costly superconducting coil systems.
What is Earth's magnetic field strength?
Earth's magnetic field strength varies by location, ranging from approximately 25 microtesla (µT) near the equator to around 65 µT near the magnetic poles. The field also changes slowly over time due to movements in the liquid outer core. The World Magnetic Model (WMM), maintained jointly by NOAA and the British Geological Survey, provides up-to-date field values for any location on Earth.
Official sources
- NIST: Special Publication 330, The International System of Units (SI).
- IEC 60050-121: International Electrotechnical Vocabulary, Electromagnetism. IEC.
- NIH National Institute of Biomedical Imaging and Bioengineering: Magnetic Resonance Imaging (MRI).
- NOAA National Centers for Environmental Information: World Magnetic Model.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.