We know that,
Magnetic flux (ϕ)=B.A(\phi)= B.A(ϕ)=B.A
Where B is the magnetic field and A is the area.
Unit of magnetic field(B) = T(Tesla)
Unit of area (A)=m2(A)=m^2(A)=m2
Hence, unit of magnetic flux =Tesla−m2=Tesla-m^2=Tesla−m2 it is also called Weber