Parallel Inductance Calculator
Enter two inductances and the parallel inductance calculator returns the equivalent inductance of the pair in henries — and shows why two coils in parallel always store less than either one alone.
Equivalent inductance instantly
Enter both coil values in henries and the calculator returns the single equivalent inductance L_eq = (L1·L2)/(L1+L2) of the parallel pair.
Use the same unit
Enter both inductances in henries. Convert millihenries (mH) by dividing by 1000 and microhenries (µH) by dividing by 1,000,000 first.
What is parallel inductance?
Two coils sharing the same two nodes
When two inductors are wired in parallel, the same voltage appears across both, and the current splits between them. The parallel inductance calculator combines the two coils into a single equivalent inductor, L_eq = (L1·L2)/(L1+L2), measured in henries. The defining feature is that the equivalent inductance is always smaller than the smaller of the two coils — adding a second parallel path gives the current another route, so the pair opposes changes in current less than either inductor would on its own. This mirrors how resistors combine in parallel, and it is the reciprocal of how inductors add in series. Designers reach for parallel inductors to obtain a value that is not available as a single standard part, to share current across several smaller coils, or to lower the effective inductance of a filter or power stage.
Enter two inductances in henries to get the equivalent parallel inductance instantly — it is always less than the smaller coil.
The equivalent inductance of two parallel coils is their product divided by their sum.
L_eq = (L1 × L2) / (L1 + L2)Take a 0.1 H coil in parallel with a 0.2 H coil. Multiply the two values to get the product, 0.1 × 0.2 = 0.02. Add them to get the sum, 0.1 + 0.2 = 0.3. Divide the product by the sum: 0.02 / 0.3 = 0.066667 H. The result (about 66.7 mH) is smaller than either original coil, exactly as expected for a parallel combination — the extra current path lowers the overall inductance.
The formula is exact for ideal coils, but a couple of practical points are worth keeping in mind.
Assumes no mutual coupling and consistent units
This calculator assumes the two coils are magnetically independent — there is no mutual coupling between them. If the inductors share a magnetic field (placed close together or on the same core), mutual inductance shifts the real value and the simple product-over-sum result no longer holds. It also ignores winding resistance and core losses. Keep both inputs in the same unit: convert mH and µH to henries before you enter them, or the answer will be off by a factor of a thousand or a million.