Inductance Calculator

This calculator finds the inductance of a solenoid from its physical dimensions and core material. It also returns the energy stored in the inductor's magnetic field at a given current, and the inductive reactance at a given frequency. Inductance is the property of an electrical conductor that opposes changes in current. When the current through an inductor changes, the changing magnetic flux induces a voltage that opposes the change, which is the principle behind Faraday's Law. The formula for a solenoid is L = mu_r x mu_0 x N squared x A / l, where mu_0 is the permeability of free space (4 x pi x 10 to the minus 7 henries per metre), mu_r is the relative permeability of the core material (1 for air or vacuum, around 200 to 5000 for iron, much higher for ferrite and mumetal), N is the number of turns, A is the cross-sectional area of the core in square metres, and l is the length of the winding in metres. Inductors are used in filters, transformers, switched-mode power supplies, chokes, and oscillator circuits. The inductive reactance is XL = 2 x pi x f x L in ohms, which is the effective resistance the inductor presents to alternating current at frequency f. At 50 Hz (NZ mains frequency), a 12.57 uH inductor has a reactance of about 0.00395 ohms. The energy stored in the magnetic field when carrying current I is E = 0.5 x L x I squared joules. Enter the solenoid dimensions and optional current and frequency values below.

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mu_0 = 4 x pi x 10^-7 H/m. Formula assumes an ideal solenoid with uniform field and no fringing effects. Real inductors differ; add 10-20% for practical designs.