Magnetic Field of a Magnet Calculator

Inputs

Magnet grade (grade)

Representative remanence values for common permanent-magnet materials. Use the supplier Br value when available.

Magnet diameter (D_m)

Diameter of the circular pole face.

Magnet thickness (L)

Axial length of the magnet in the magnetization direction.

Distance from pole face (z)

Distance measured outward from the magnet pole face along the symmetry axis.

Default result

Axial magnetic field(B_z)

171.5mT

Pass

Also computed

Axial field(B_z)0.1715T

Axial field(B_z)1,715G

Pole-face field(B_0)295.2mT

Field vs pole face(B_z/B_0)58.11%

Remanence used(B_r)1.32T

Thickness / diameter(L/D)0.25

The field falls quickly with distance from the pole face. This curve is along the magnet axis only; off-axis fields are not represented.

Method notes 3 notes

Uses the closed-form on-axis field for an axially magnetized cylinder: B = Br/2*((L+z)/sqrt(R^2+(L+z)^2) - z/sqrt(R^2+z^2)).
The result is only for the symmetry axis outside one pole face. Off-axis fields, nearby steel, keeper plates, arrays and demagnetization need field solving or measurement.
Grade Br values are representative. Temperature, tolerance, magnetization quality and vendor grade data can shift the real field.