# Encyclopedia Magnetica

### Site Tools

calculator:effective_permeability_from_air_gap

### Calculator of effective magnetic permeability from air gap

For a magnetic circuit with uniform cross-section the value of effective permeability μeff can be calculated if the lengths and permeabilities of both parts are known.

 $$\mu_{eff} = \frac{\mu_{core}}{ {\frac{l_{gap}}{l_{core}} ⋅ \mu_{core} + 1 } }$$ (unitless)

Relative μcore = (unitless)       core length lcore =       gap length lgap =

Effective permeability = (unitless)

Note: The equation is valid only for a simple magnetic circuit, with cross-sectional area of the core and gap being equal, for relative permeability if lcore » lgap, and if µcore » 1.