The inductance \(L\) of a coil is defined in relation to the magnetic flux \(\phi_B\) passing through it when it is energized by a current of intensity \(I\). By definition,
\[\phi_B=L I\]The method consists in assuming that the coil is equivalent to an assembly of regularly spaced circular turns and calculating the magnetic flux produced by each turn through itself and all the others, then summing these different fluxes.