Smoothing inductance
Forward Type Converter - magnetic sizing

As mentioned in the introduction, we also propose to relate the electrical quantities of the current-smoothing inductance of a forward converter to its geometrical dimensions.

An inductance is characterized by its value (in henrys), by the current flowing through it and by the energy it is capable of storing.

Here, energy plays the same role as power in transformer sizing: it determines the volume of the inductor. In fact, there's a direct relationship between the energy an inductor can store and its volume.