The standard international unit used to measure inductance is the henry. An inductor with a value of one henry would be fairly large and heavy, especially if intended to carry a lot of current (because it will need heavier wire). Typical inductors are much smaller than one henry and fall in the millihenry (mH) and micro Henry (μH) ranges.

Inductance is affected by how much wire is in the coil and how close the turns are to each other. If you add more wire, by either making the diameter of the coil larger or adding more turns of wire, the inductance increases. Placing the turns closer together also increases the inductance. Adding a soft iron1 core will further concentrate the magnetic field and increase the inductance.

Iron cores may be made of ferrite or laminated plates of silicon steel. Ferrite is a mixture of iron powder and a ceramic material that can be molded into convenient shapes. Variable inductors often have a screw- shaped ferrite core. The core is turned with a suitable tool and screws in or out of the coil to change the inductance.

Inductance is affected by the following properties: