# Permeability of free space

The permeability of free space, μ0, is a physical constant used often in electromagnetism. It is taken to have the exact value of 4π x 10-7 N/A2 (newtons per ampere squared).[1] It is connected to the energy stored in a magnetic field, see Hyperphysics for specific equations.

It is related to the speed of light by the equation

$c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$

where