A physical quantity representing the distribution of magnetic field. The magnetic flux D φ passing through a bin dS somewhere in the magnetic field is defined as the product of the magnitude b of the magnetic induction intensity and the projection dSCOS θ of DS in the direction perpendicular to B, that is, where θ is the included angle between the normal direction n of the bin and the magnetic induction intensity b.. The magnetic flux is scalar, θ.

Generally speaking, the magnetic flux is defined by the integral of the magnetic field on the surface area (see Figure 1 and Figure 2).

Where φ is the magnetic flux, b is the magnetic induction intensity, s is the curved surface, B dS is the dot product, and dS is the infinitesimal vector (see surface integral).

Magnetic flux is usually measured by fluxmeter. The fluxmeter comprises a measuring coil and a circuit for estimating the voltage change on the measuring coil so as to calculate the magnetic flux.