Flux is the rate of flow of particles through a given surface.
Magnetic flux (Φ) is measure in Webers.
Φ = BA
B = magnetic flux density
A = Area through which the flux passes perpendicularly
Flux at an angle
If the area is not perpendicular to the flux, it can be calculated by finding the vertical component of the flux.
Φ = BA cosθ
Where θ is the angle between the flux and the normal to the area.