Introduction
Magnetic field strength (flux density) is measured in tesla (T) or gauss (G). One tesla is exactly 10,000 gauss. Earth's surface field is ~50 microtesla (0.5 G). An MRI machine is 1.5-3 T (15,000-30,000 G). A neodymium magnet can reach 1.4 T at the pole. This calculator swaps between the two conventions without arithmetic.
Why magnetic field strength units exist and how they diverged
The tesla (T) is the SI unit, adopted in 1960. The gauss (G), older and CGS, persists in physics labs, speaker and motor specs, and geomagnetism. Nikola Tesla and Carl Friedrich Gauss — two units for the same physical quantity, honoring two different physicists.
MRI naming: a '3T' machine runs at 3 tesla = 30,000 gauss. Earth's field at the surface averages 25-65 microtesla (0.25-0.65 G), varying by location and slowly drifting. The gauss/oersted distinction matters for ferromagnetic materials: gauss measures the flux density inside material, oersted measures the field strength.
How to convert magnetic field strength
Tesla to gauss: multiply by 10,000. Gauss to tesla: divide by 10,000. Earth field: 50 µT = 0.5 G. MRI 3T = 30 kG. Neodymium magnet: 1.4 T = 14,000 G at the surface.
Units supported by this magnetic field strength calculator
- Tesla (T)
- Millitesla (mT)
- Microtesla (µT)
- Nanotesla (nT)
- Gauss (G)
- Milligauss (mG)
- Kilogauss (kG)
- Gamma
Common magnetic field strength conversion mistakes
- Tesla vs gauss prefix confusion. 100 mT = 1,000 G (millitesla converts to gauss × 10); 1 µT = 0.01 G. Always convert carefully with prefixes.
- Flux density vs total flux. Flux density (T, G) is per area. Total flux is the whole field through a loop — units are weber (Wb) or maxwell (Mx). 1 Wb = 10⁸ Mx. The magnetic flux unit is different from the flux density.
- Field measurements affected by nearby objects. A steel tape measure near the magnetometer distorts the reading. Get clear of ferromagnetic material for accurate measurements.
- Earth field orientation. The field points mostly downward in the Northern Hemisphere (into the ground) and upward in the Southern. A compass needle hangs if gimbaled in the field direction.
Real-world magnetic field strength examples
- Earth's surface magnetic field: 25-65 µT (0.25-0.65 G) depending on location.
- Refrigerator magnet (ferrite): 5 mT (50 G).
- Strong rare-earth magnet (neodymium N52): 1.4 T (14,000 G) at pole face.
- MRI scanner: 1.5 T (standard clinical), 3 T (advanced clinical), 7 T (research).
- Speaker voice coil field: 1-1.5 T.
- Particle accelerator dipole magnets (LHC): 8.3 T.
- Strongest continuous field in lab: 45 T (hybrid magnet).
- Pulsed-field magnets (non-destructive): up to 100 T for milliseconds.
- Neutron star surface: ~10⁸ T.
- Magnetar surface: up to ~10¹¹ T.
Tips for accurate magnetic field strength conversion
- Keep credit cards and hard drives away from rare-earth magnets. Even a 1.4 T magnet can erase a magnetic stripe at contact.
- MRI safety: nothing ferromagnetic in the room. Pens, oxygen tanks, stethoscopes become projectiles in a 3T field.
- Smartphone magnetometers read to microtesla resolution but are affected by nearby metal and other phones.
Related: Magnetic Flux Converter · Electric Current Converter · Inductance Converter.