Inductor Network Calculator

This inductor network calculator combines up to five inductors wired in series or parallel into a single equivalent inductance (L_eq). If you enter a current, it also estimates the magnetic energy stored in that equivalent inductance under the ideal relation used by the page. That makes it useful when you are assembling a filter leg, checking a resonant tank, comparing coils you already have on hand, or deciding whether a series chain or parallel bank gets you closer to a target value before you build the circuit.

What this inductor network calculator outputs

• Equivalent inductance of the network (L_eq, in henries).
• Stored energy (optional) if you enter current (E, in joules), computed from L_eq and I.

Units for inductor values

Inductance is measured in henries (H), but most real inductors are labeled in smaller units such as millihenries, microhenries, or nanohenries:

• 1 mH = 10⁻³ H
• 1 µH = 10⁻⁶ H
• 1 nH = 10⁻⁹ H

Enter all inductors in henries. Examples:

• 47 µH = 47 × 10⁻⁶ H = 0.000047 H
• 2.2 mH = 2.2 × 10⁻³ H = 0.0022 H

When you are translating a datasheet value, convert it once and then paste the result into the matching field. The calculator does not infer prefixes, so a coil marked 47 µH must be entered as 0.000047 H, not as 47.

Formulas used for series and parallel inductors

The calculator treats the set of inductors as an ideal series or ideal parallel network, so the formula changes with the wiring you choose. Use the arrangement that matches the actual circuit, because a series chain and a parallel bank push the equivalent inductance in opposite directions.

Inductors in series

For series inductors, the same current flows through each inductor and the voltages add. The equivalent inductance is the sum:

In plain terms, the series setting adds every positive inductor value you enter, and blank boxes are ignored. This is the right model when the same current must pass through each coil in sequence and you want the total to rise in a predictable way.

Inductors in parallel

For parallel inductors, each branch sees the same voltage and the current splits among branches. The reciprocals add:

1 / L_eq = Σ (1 / L_i)

Then:

L_eq = 1 / Σ (1 / L_i)

This is the right model when several coils share the same nodes and divide the current. A very small inductance in one branch can pull the total downward quickly, so it is worth checking the entered units before you trust the result.

Energy stored (optional)

If you enter a current, the tool estimates stored magnetic energy using the equivalent inductance rather than trying to model each coil separately:

E = ½ · L_eq · I²

Where E is joules (J), L_eq is henries (H), and I is amperes (A). This is only an ideal estimate, but it is still useful for comparing how much energy a higher-current operating point would store in the same network.

How to interpret the inductor-network results

• Series raises the total inductance: adding inductors in series increases L_eq directly, and two identical inductors in series simply double the inductance. That makes series the straightforward choice when you are trying to reach a higher target with parts you already have.
• Parallel lowers the total inductance: adding parallel branches decreases L_eq, and two identical inductors in parallel give half the inductance of one part. That is useful when you need a smaller value or want to spread current across several coils.
• Energy depends strongly on current: because energy scales with I², a modest increase in current can have a much larger effect on the stored-energy estimate than a similar change in inductance. If the current input changes, recheck the result before comparing two designs.

Worked example: three inductors in parallel with a 2 A current

This example shows how the inductor-network rules behave when you place three different coils in parallel and then estimate the stored magnetic energy from the equivalent inductance.

Three inductors in parallel:

• L₁ = 10 mH = 0.010 H
• L₂ = 20 mH = 0.020 H
• L₃ = 40 mH = 0.040 H

Compute the reciprocal sum:

• 1/L₁ = 1/0.010 = 100 H⁻¹
• 1/L₂ = 1/0.020 = 50 H⁻¹
• 1/L₃ = 1/0.040 = 25 H⁻¹

Sum = 100 + 50 + 25 = 175 H⁻¹

Take the reciprocal:

L_eq = 1 / 175 ≈ 0.005714 H = 5.714 mH

If the network current is I = 2 A, the stored energy estimate is:

E = ½ · 0.005714 · (2)² = 0.5 · 0.005714 · 4 ≈ 0.011428 J

So the network stores about 0.0114 joules at 2 A under the ideal assumptions below.

Series vs. parallel in this inductor network: quick comparison

Assumptions and limitations for real inductor networks

• Ideal inductors: the calculation ignores winding resistance (DCR), core losses, parasitic capacitance, and skin or proximity effects, so the result is a clean circuit-model value rather than a full physical prediction.
• No mutual coupling: the page assumes the inductors do not magnetically couple. If coils are near each other or share a core, coupling can increase or decrease the effective inductance and the simple series or parallel rules may no longer apply.
• No saturation: real inductors lose inductance as current approaches saturation. The energy result is therefore only an estimate, and it can look optimistic in high-current designs.
• Frequency dependence not modeled: inductance and loss both vary with frequency, so fast-switching converters and RF circuits can behave differently from this ideal network model.
• Tolerance not included: part tolerances such as ±10% or ±20% and temperature drift can shift the true equivalent inductance enough to matter when the target value is tight.
• Parallel edge cases: extremely small entered inductance values, approaching 0 H, will dominate the reciprocal sum and drive L_eq toward 0. In a real circuit that usually points to a near-short inductive reactance at the modeled frequency, which is rarely an ideal operating condition.
• Using fewer than five inductors: leave unused fields blank; only the values you enter are counted as part of the network.

If you need accuracy for tightly coupled inductors, gapped cores, or high-current builds, treat the result as a first-pass check and verify it with datasheets, measurement, and, when necessary, a coupled-inductor model.

How to use this inductor network calculator

1. Choose Series when the inductors are connected end to end, or choose Parallel when they share the same two nodes.
2. Enter each inductance in henries, converting from microhenries or millihenries before you type the value.
3. Leave any unused inductor fields blank so the calculator ignores those positions.
4. If you want the energy estimate, enter the operating current in amperes.
5. Run the calculation and compare the result with the other wiring arrangement before you commit to a final coil layout.