The permeability constant or magnetic constant (μ₀) is the permeability of vacuum (or of free space). It is a physical constant not defined by other physical constants.

It is defined as the ratio of magnetic field density to magnetic field strength in vacuum:

$\backslash mu\_0\; =\; \backslash frac\{\backslash mathbf\{B\}\}\{\backslash mathbf\{H\}\}$

In SI units, the value is exactly expressed by:

μ₀ = 4π×10⁻⁷ N/A² = 4π×10⁻⁷ H/m

References

Physical constants

Constante magnétique