# Field strength

# What is the governing equation for field strength versus distance?

For a round magnet with a radius of R and length L, the field Bx at the centre line of the magnet at a distance X from the surface can be calculated according to the following formula, where Br is the residual induction of the material:

There are additional formulas that can be used to calculate the field from a rectangular magnet and magnets in other configurations.