In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to a magnetic field. Absolute permeability is represented by the symbol μ. In SI units, permeability is measured in henrys per metre. <math>\mu_0 \,<math> is known as the Permeability of free space (absolute permeability below)

Permeability in linear materials owes its existance to the approximation:

<math> \mathbf{M}=\chi_m\mathbf{H}<math>

Where <math>\chi_m \,<math> is a dimensionless scalar called the Magnetic Susceptibility

According to the definition of the Auxillary Field, <math>\mathbf{H}<math>

<math>\mathbf{B}=\mu_0 (\mathbf{H}+\mathbf{M})=\mu_0 (1 + \chi_m)\mathbf{H}<math>

<math>\mu=\mu_0(1+ \chi_m) \,<math>

Thus <math>\mu = \frac {B} {H} \,<math>

where

μ is the permeability, measured in henrys per metre

B is the magnetic flux density (also called the magnetic induction) in the material, measured in teslas

H is the magnetic field strength, measured in amperes per metre

Absolute permeability

Absolute permeability is represented by the symbol μ₀ and is the permeability of the vacuum, where μ₀ = 4π × 10⁻⁷ N A⁻² (exactly).

Together with permittivity, permeability defines the speed of light.

Relative permeability

Relative permeability, sometimes denoted by the symbol μ_r, is the ratio of the permeability of a specific medium to the permeability of free space μ₀:

<math>\mu_{r} = \frac{\mu}{\mu_{0}} <math>

Relative permeability for some materials
Medium	<math>\chi_m = \mu_r - 1 \,<math>
Hydrogen	0.008 × 10-6
Copper	−6.4 × 10-6
Water	−8.0 × 10-6
Aluminium	22.2 × 10-6
Platinum	265 × 10-6

SI magnetism units

SI electromagnetism units edit  (http://www.wordiq.com/definition/Template:SI_electromagnetism_units)
Name	Symbol	Dimensions	Quantity
ampere (SI base unit)	A	A	Current
coulomb	C	A�s	Electric charge, Quantity of electricity
volt	V	J/C = kg�m2�s−3�A−1	Potential difference
ohm	Ω	V/A = kg�m2�s−3�A−2	Resistance, Impedance, Reactance
ohm metre	Ω�m	kg�m3�s−3�A−2	Resistivity
farad	F	C/V = kg−1�m−2�A2�s4	Capacitance
farad per metre	F/m	kg−1�m−3�A2�s4	Permittivity
reciprocal farad	F−1	kg1�m2�A−2�s−4	Elastance
siemens	S	Ω−1 = kg−1�m−2�s3�A2	Conductance, Admittance, Susceptance
siemens per metre	S/m	kg−1�m−3�s3�A2	Conductivity
weber	Wb	V�s = kg�m2�s−2�A−1	Magnetic flux
tesla	T	Wb/m2 = kg�s−2�A−1	Magnetic flux density
ampere per metre	A/m	m−1�A	magnetic induction
ampere-turns per weber	A/Wb	kg−1�m−2�s2�A2	Reluctance
henry	H	V�s/A = kg�m2�s−2�A−2	Inductance
henry per metre	H/m	kg�m�s−2�A−2	Permeability
(dimensionless)	-	-	Magnetic susceptibility

ca:permeabilitat de:Permeabilit�t (Magnetismus) ja:透磁率 sl:magnetna permeabilnost