In magnetics, the ratio of the density of the magnetic flux, B (in units of teslas), to the strength of the magnetic field, H (in units of amperes/meter), typically in units of H/m.
μ = B / H,
μ = magnetic permeability
B = magnetic flux or magnetic induction
H = magnetizing field strength.
μ = μ0 = 4π × 10−7 henries per meter (H/m) is the magnetic permeability of free space, or a vacuum. For practical purposes, the magnetic permeability of air or water is μ0.