Magnetic flux is defined as the number of magnetic lines of force passing normally through a surface. It is denoted by symbol Φ (phi). The S.I. unit of magnetic flux is weber (Wb). It is a scalar quantity. The CGS unit of magnetic flux is maxwell. Consider a surface having area, A in the magnetic field having magnetic flux density, 
as shown in figure 1.
Mathematically, Magnetic flux is defined as the scalar product between the magnetic flux density () and the vector of the surface area (
).
where,
= magnetic flux
B = magnetic flux density magnitude
A = area of surface
θ = angle between and
Note: The direction of the vector is always normal to the surface.
Case-1: When θ = 0°
In this case, the flux is maximum.
Case-2: When θ = 90°
In this case, the flux is minimum.
Note: Magnetic flux is usually measured with a fluxmeter.
