What is Magnetic Flux Density

What is magnetic flux density? Magnetic Flux density is the measure of the number of magnetic lines of force per unit of cross-sectional area.

As a rule, B is used to represent magnetic flux density, and Wb/m2 is the SI unit for measuring it. The unit of measure for magnetic induction is the tesla, which is equal to one weber per square meter (T).

It is possible to calculate the flux density given the total flux and the magnetic path area by using the formula:

B = Φ / A


B = flux density in tesla (Wb/m2)
Φ = total flux in webers
A = area in m2

Example of Magnetic Flux Density

The flux density in a magnetic circuit is 0.01T, and its cross-sectional area is 100mm2. Learn how much total flux the circuit has.

Φ = BA (1)
= 0,01 x 100E – 6 (2)
= AE-6wb (ans) (3)

Please take note that the answer is given in webers, not lines of force.

Example of Magnetic Flux Density 2

There is 0.65 Wb of flux at the center of an air-core coil. If the diameter of the core is 4 cm, then determine the flux density.


The initial step is to determine the central region’s surface area:

figure 1
figure 1

At this point, we can use the following formula to determine the magnetic flux density:

figure 2
figure 2