The Magnetic flux Φ through any surface held in a magnetic field b is measured by the total number of magnetic lines of force crossing the surface
where d S = small area element through which line is passing.
The S.I. unit of magnetic flux is weber (Wb). One weber is the amount of magnetic flux crossing over an area of 1 metre2 held normal to a uniform magnetic field of one tesla.
Thus 1 weber = 1 tesla x 1 m2
The c.g.s. unit of Φ is maxwell (Mx),
where 1 weber = 108 maxwell
Reference: This article is referred from my authored book “electrical engineering materials”.