Neodymium Magnets and Magnetic Flux Density
Magnetic flux density (B) describes how concentrated a magnetic field is: think of it as how many field lines pass through a given area. It’s measured in tesla (T) or gauss (G), where 1 T = 10,000 G. Neodymium magnets have very high flux density: an N52 grade holds about 1.4 to 1.5 T inside the material, and a few thousand gauss at its surface.
Units at a Glance
| Unit | Symbol | Equals |
|---|---|---|
| Tesla | T | 10,000 gauss |
| Millitesla | mT | 10 gauss |
| Gauss | G | 0.1 millitesla |
| Kilogauss | kG | 1,000 gauss = 0.1 tesla |
What Sets a Magnet’s Flux Density?
Grade
Higher grades have higher remanence (Br). N52 material reaches about 14,300 to 14,800 G.
Shape
Thicker magnets, relative to their width, keep more flux at the surface.
Distance
Flux density falls off quickly as you move away from the pole face.
Flux, Flux Density and Field Strength
These terms are related but different:
- Magnetic flux (Φ) is the total amount of field passing through an area, in webers (Wb).
- Flux density (B) is flux per unit area, in tesla or gauss. A gaussmeter measures this.
- Field strength (H) describes the magnetizing force, in oersteds or A/m. It’s used mostly by magnet engineers.
See our magnet glossary for more definitions.
How Safety Standards Use Flux Density
Toy safety standards such as ASTM F963 rate the hazard of small magnets with a flux index: the square of the surface flux density (in kG) times the pole area (in mm²). Magnets small enough to swallow with a flux index above 50 kG²·mm² are considered hazardous in children’s toys, because two swallowed magnets can attract each other through the intestines.
Keep Magnets Away from Children
Our magnets are not toys. Keep them out of reach of children and pets. If you suspect someone has swallowed a magnet, seek medical care right away.