High Quality Content by WIKIPEDIA articles! Vacuum permeability, permeability of free space, or magnetic constant is an ideal, (baseline) physical constant, which is the value of magnetic permeability in a classical vacuum, and this type of vacuum is merely an abstraction from nature. Vacuum permability is derived from production of a magnetic field by an electric current or by a moving electric charge and in all other formulas for magnetic-field production ,in a vacuum. When the permeability is that of the vacuum, denoted µ0 has an exact defined value.