Inductors in Parallel Calculator
Enter two or more inductor values to find the total equivalent inductance of a parallel circuit. Add up to eight inductors, switch between H, mH, uH and nH, enter a frequency to get inductive reactance, and use the reverse-solve mode to find a missing inductor value that gives a specific target inductance. The step-by-step panel shows the full working with your actual numbers.
Formula
Worked example
Three inductors of 10 mH, 10 mH, and 10 mH in parallel: 1/Leq = 1/10 + 1/10 + 1/10 = 0.3 mH⁻¹, so Leq = 1/0.3 = 3.33 mH. For two unequal inductors of 5 mH and 15 mH: 1/Leq = 1/5 + 1/15 = 0.267 mH⁻¹, Leq = 3.75 mH.
What is inductance and why does it decrease in parallel?
Inductance measures how strongly a coil opposes changes in current by generating a back-EMF. When you connect inductors in parallel, the total current splits across multiple branches, so each branch sees a smaller fraction of the total current change. The combined effect is a lower opposition to current change than any single coil alone, which means a lower equivalent inductance. This is the same reason parallel resistors produce a lower resistance: more paths, less opposition. The rule is that the equivalent inductance is always less than the smallest inductor in the parallel combination.
The parallel inductance formula
The reciprocal formula is the key tool: 1/Leq = 1/L1 + 1/L2 + ... + 1/Ln. Invert the sum to get Leq. For the special case of n equal inductors each with value L, the formula simplifies neatly to Leq = L/n. For only two inductors, the product-over-sum shortcut is Leq = (L1 x L2) / (L1 + L2). This calculator applies the full reciprocal formula for any number of inductors up to eight, so you never have to chain the two-inductor shortcut manually.
Mutual inductance and magnetically coupled coils
The formula on this page assumes the inductors are not magnetically coupled, meaning no flux from one coil links with another. When two coils share a magnetic field, mutual inductance M modifies the result. For two inductors with mutual inductance M, the equivalent inductance becomes L1L2 - M^2 / (L1 + L2 - 2M) when both currents enter the dotted terminals (aiding coupling) and L1L2 - M^2 / (L1 + L2 + 2M) when they enter opposing terminals. To avoid coupling effects in practice, orient toroidal inductors at right angles to each other, use shielded inductors, or space them at least one diameter apart on the PCB.
Inductive reactance and frequency
Inductors are frequency-dependent: their opposition to AC current, called inductive reactance, increases with frequency. The formula is XL = 2 x pi x f x Leq, where f is the signal frequency in hertz and Leq is the equivalent inductance in henries. A smaller parallel equivalent inductance means lower reactance at any given frequency, which is sometimes exactly what a filter or matching network needs. Enter a frequency in the optional field to see the reactance of your parallel combination alongside the inductance result.
Practical uses of parallel inductors
Parallel inductor combinations appear in several real circuit scenarios. Power designers parallel multiple smaller inductors instead of one large one to increase current-handling capacity, distribute heat, and take advantage of smaller off-the-shelf parts. Filter designers use parallel combinations to fine-tune cut-off frequencies when the exact inductance value is not available in standard E-series. RF engineers may parallel inductors to achieve very small equivalent inductances (in the nH range) that would otherwise require impractical single-component solutions at high frequency. The reverse-solve mode on this calculator helps you find what inductance value you need to add in parallel to hit a precise design target.
Common inductor unit prefixes
| Unit | Symbol | Value in Henries | Typical application |
|---|---|---|---|
| Henry | H | 1 H | Power electronics, large EMI chokes |
| Millihenry | mH | 0.001 H | Audio crossovers, DC-DC converters |
| Microhenry | uH | 0.000001 H | RF circuits, switch-mode power supplies |
| Nanohenry | nH | 0.000000001 H | High-frequency RF, PCB trace inductors |
Quick reference for converting between common inductance scales.
Frequently asked questions
Why is equivalent inductance always less than any single inductor?
Each parallel branch provides an additional path for current to flow. More paths means the total magnetic flux linkage produced by a given total current is lower, so the circuit stores less energy per ampere of current, which is what a lower inductance means. Mathematically, adding another positive term to the sum of reciprocals always increases the sum, and inverting a larger number gives a smaller result.
What happens if I connect two identical inductors in parallel?
Two equal inductors each with value L connected in parallel give an equivalent inductance of L/2. Three equal inductors give L/3, and so on. This is the same halving rule as equal resistors in parallel, and it makes quick mental estimates easy when you are using matched components.
How does parallel inductance differ from parallel capacitance?
Capacitors in parallel add directly: Ctotal = C1 + C2 + ... + Cn. Inductors in parallel use the reciprocal formula: 1/Leq = 1/L1 + 1/L2 + ... + 1/Ln. The behaviors are opposite in this respect. Inductors in parallel behave like resistors in parallel, while inductors in series behave like resistors in series. Capacitors are the mirror image: series capacitors use the reciprocal rule, while parallel capacitors add directly.
What does mutual inductance do to the parallel result?
If two inductors share a magnetic field, mutual inductance (M) changes the equivalent inductance. Aiding coupling (both currents entering dotted terminals) increases the effective self-inductances, raising Leq compared with the non-coupled case. Opposing coupling decreases Leq. This calculator assumes no mutual coupling (M = 0), which is accurate for physically separated inductors with minimal overlapping fields.
Can I use this calculator for inductors in different units?
Yes. Select the unit (H, mH, uH, or nH) that matches your values and enter all inductors in that unit. The calculator converts internally to henries, computes the result, and displays it back in your chosen unit. If your inductors are in mixed units, convert them all to the same scale before entering them, or choose a unit that accommodates all values.
What is the reverse-solve mode?
Reverse-solve lets you specify a target equivalent inductance and your known inductors, then calculates what value the missing inductor must have. This is useful when you know the design target and have some components on hand but need to find the remaining piece. Switch the "Calculate" dropdown to "Find missing inductor", enter the target and the known values, and the result tells you exactly what the unknown inductor should be.