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Inductors in Parallel Calculator

Enter two or more inductor values to get the parallel total.

How it is calculated

Enter between two and four inductances in the fields l1 to l4. The tool adds their reciprocals and inverts the sum: 1/Lt = 1/L1 + 1/L2 + … , so Lt = 1 / Σ(1/Li). The number is treated as henries (H) and the answer is printed in henries with six decimals, along with how many values were used. Empty fields are skipped, so you can leave l3 or l4 blank; fewer than two filled fields give no result, and any value that is zero or negative cancels the result. Mutual coupling between coils is ignored, so the answer holds only for coils that do not share magnetic flux.

Worked example

Three chokes of 10 mH, 22 mH and 47 mH are typed in henries as 0.01, 0.022 and 0.047. Reciprocals: 1/0.01 = 100, 1/0.022 = 45.4545 and 1/0.047 = 21.2766, which add up to 166.7311. Inverting gives 1 / 166.7311 = 0.005998 H, about 6.0 mH, from 3 inductors. It is smaller than the smallest part (10 mH), as it must be for a parallel combination.

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Common mistakes

  • Typing millihenries or microhenries as if they were henries. A 10 mH coil must be entered as 0.01, not 10, otherwise the total is 1000 times too large.
  • Mixing units between fields, for example 10 in one field meaning mH and 0.022 in another meaning H.
  • Expecting the total to be larger than the parts. Parallel inductance always falls below the smallest inductor; if you want the sum, you need the series formula instead.
  • Using the result for coils wound close together or on a shared core. The formula assumes no mutual inductance, so the real value can differ noticeably.
  • Entering a 0 for an unused slot. Zero is rejected and wipes the result; leave unused fields empty.

About this calculator

When two or more inductors are wired in parallel with no mutual coupling between them, their combined inductance follows the same reciprocal-sum pattern as resistors in parallel: 1/Lt = 1/L₁ + 1/L₂ + ... + 1/Ln. That means the total inductance is always smaller than the smallest individual inductor in the group — each added parallel path lets a changing current split across more coils, so the combination opposes a change in current less than any single inductor does.

This calculator takes two to four inductor values and returns the total parallel inductance using that formula. Electronics hobbyists building filters or resonant circuits, and RF and power electronics engineers use it when designing circuits that need a specific combined inductance not available as a single off-the-shelf component, or when analyzing how paralleled chokes will behave together — keeping in mind that the formula assumes negligible mutual inductance, which doesn't hold if the coils are wound close enough to couple magnetically.

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Comments (1)

  • Editorial team

    Values must be typed in henries, so 47 mH is 0.047, and the answer is printed to six decimals. That means a very small result, such as the parallel combination of two 100 nH parts (0.0000001 H), displays as 0.000000 H. For nanohenry-range work, scale your values up consistently, read the result, then scale back. Do you usually work in mH, uH or nH?

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