The tesla (symbol T) is the SI derived unit of magnetic flux density, commonly denoted as B. One tesla is equal to one weber per square metre, and it was named in 1960 in honour of Nikola Tesla. The strongest fields encountered from permanent magnets are from Halbach spheres which can be over 4.5 T. The strongest field trapped in a superconductor in a lab as of July 2014 is 17.6 T. The record magnetic field has been produced by scientists at the Los Alamos National Laboratory campus of the National High Magnetic Field Laboratory, the world's first 100 Tesla non-destructive magnetic field.
A particle carrying a charge of 1 coulomb and passing through a magnetic field of 1 tesla at a speed of 1 meter per second perpendicular to said field experiences a force with magnitude 1 newton, according to the Lorentz force law. As an SI derived unit, the tesla can also be expressed as
In the production of the Lorentz force, the difference between these types of field is that a force from a magnetic field on a charged particle is generally due to the charged particle's movement while the force imparted by an electric field on a charged particle is not due to the charged particle's movement. This may be appreciated by looking at the units for each. The unit of electric field in the MKS system of units is newtons per coulomb, N/C, while the magnetic field (in teslas) can be written as N/(C·m/s). The dividing factor between the two types of field is meters/second (m/s), which is velocity. This relationship immediately highlights the fact that whether a static electromagnetic field is seen as purely magnetic, or purely electric, or some combination of these, is dependent upon one's reference frame (that is: one's velocity relative to the field).
In ferromagnets, the movement creating the magnetic field is the electron spin (and to a lesser extent electron orbital angular momentum). In a current-carrying wire (electromagnets) the movement is due to electrons moving through the wire (whether the wire is straight or circular).