Relative magnetic permeability

Relative magnetic permeability is defined as the ratio of permeability of medium (μ) to the permeability of free space (μ₀)

μ_r = μ/μ₀

or                                 μ_r = B/H/(B₀/H)

or                                 μ_r = B / B₀

is permeability of free space.