Inductors in Parallel Calculator

How to use the parallel inductors calculator

What this calculator does

This calculator evaluates the ideal equivalent inductance of positive, uncoupled inductors connected in parallel. It can also rearrange the same identity to find one unknown branch when you know the desired equivalent inductance and the remaining branches. The calculation assumes that magnetic coupling between coils is negligible. That distinction matters: nearby coils can share magnetic flux, and then mutual inductance changes the circuit equations. For an introduction to why parallel inductance becomes smaller than the individual branches, see the LibreTexts discussion of series and parallel inductors.

When to use it

Use it when checking a parallel inductor network on a schematic, comparing component substitutions, estimating the equivalent value created by several uncoupled branches, or back-solving the branch inductance needed to hit a specified equivalent value. It is not a magnetic-coupling simulator, a saturation model, an impedance calculator, or a substitute for a component datasheet at a particular frequency.

How to calculate

1. The calculator opens with a complete demonstration: Inductor 1 = 5 H, Inductor 2 = 10 H, and Inductor 3 = 15 H. The result and a validated example Excel workbook are available immediately.
2. Use Calculate to choose Equivalent inductance or a particular inductor. For an unknown branch, enter the Target equivalent inductance; the selected branch becomes the solved value.
3. Replace the inductor values, choose each branch Unit, and use Add inductor or the remove buttons as needed. Up to ten branches are supported. Changing a branch unit converts the entered number so the physical inductance stays the same.
4. Choose the Result unit you want to read and export. The live result, summary metrics, and branch table all update from the same canonical calculation.
5. Select Download Excel to export the current validated state as an .xlsx workbook. Reset clears the demonstration and user-entered data; after reset, Excel export stays disabled until a complete valid state exists again.

Input guide

Calculate is a required mode selection. “Equivalent inductance” treats every populated branch as a known positive inductance. Choosing “Inductor 1” through “Inductor 10” asks the calculator to solve that one branch from the target equivalent and the other known branches. A common mistake is selecting a branch to solve while entering a target equivalent that is not physically compatible with the known branches.

Target equivalent inductance appears only when solving an individual branch. Enter a positive decimal number using a period as the decimal separator; scientific notation and grouped numbers are intentionally rejected. Pick its adjacent unit from nH, µH, mH, H, or kH. For example, 2 mH is valid. The target must make the unknown reciprocal positive; otherwise no finite positive unknown inductor can satisfy the ideal parallel identity.

Inductor 1 through Inductor 10 are positive decimal inductance values. Blank non-solved rows are ignored, so one populated inductor is enough to reproduce its own equivalent value. Each row has a required Unit selector. Example values include 5 H, 220 µH, or 3.3 mH. Adding another positive parallel branch increases the reciprocal sum and therefore lowers the equivalent inductance. Zero, negative numbers, commas, scientific notation, and nonnumeric text are rejected rather than silently coerced.

Result unit controls presentation, not physics. Choose nH, µH, mH, H, or kH. Internally the model converts every value to henries before applying the formula. The henry is the SI derived unit of inductance; NIST lists the henry among the SI derived units with special names in its Guide to the SI.

Output guide

Equivalent inductance is the primary result in equivalent mode; when solving a branch, the primary label changes to the required inductor. Active branches and Branch count report how many finite positive branch values participate in the final model. Smallest branch shows the minimum participating inductance. Reciprocal sum is the sum of the 1/L terms in reciprocal henries and is the direct denominator of the equivalent-inductance identity. Model states “Uncoupled” to remind you of the core assumption.

The Branch calculation detail table lists each participating Branch, whether its Role is Known or Solved, its displayed Inductance, its canonical Inductance (H), and its Reciprocal contribution (1/H). A reciprocal contribution of zero never appears for a valid branch because zero inductance is outside this calculator's supported domain. The reciprocal values are exact calculation terms, not percentages or recommendations.

Worked example

With the startup values 5 H, 10 H, and 15 H, the reciprocal sum is 1/5 + 1/10 + 1/15 = 0.3666666667 1/H. Taking the reciprocal gives 2.727272727 H, displayed here as 2.727273 H. That result is lower than the smallest branch, 5 H, as expected for more than one positive uncoupled inductor in parallel. The workbook generated from the first-open state carries the same inputs and result values.

Learn more

The basic relation follows from equal voltage across parallel branches and the inductor relation between voltage and current change. For the unit itself, the BIPM's definition of the henry ties one henry to one volt generated by a current changing at one ampere per second.