Just like resistors or capacitors, you can combine inductors in series or parallel within an electronic circuit. Then you can use simple equations to calculate the total inductance of the circuit. Note, however, that for the calculations to be valid, the inductors must be shielded.

If the inductors aren't shielded, they'll not only be affected by their own magnetic fields but also by the magnetic fields of other inductors around them. In that case, all bets are off.

You calculate inductor combinations just like resistor combinations, using exactly the same formulas except substituting henrys for ohms. Here are the formulas:

  • Series inductors: Just add up the value of each individual inductor.

  • Two or more identical parallel inductors: Add them up and divide by the number of inductors.

  • Two parallel and unequal inductors: Use this formula:

  • Three or more parallel and unequal inductors: Use this formula:


Here's an example in which three inductors valued at 20 mH, 100 mH, and 50 mH are connected in parallel:


In this example, the total inductance of the circuit is 12.5 mH.