The flux density is defined as the measure of the number of magnetic lines of force that pass through a cross-sectional area. This is used to help to describe any area that is passed through any magnetic field. Magnetic flux can be measured using a magnetometer, in the same way as it is used for measuring magnetic fields. The total amount of the flux produced by a magnet is important to understand how dense or concentrated the flux is, per unit of planar area. So, the flux per unit of cross-sectional area is called flux density.