Calculate inductance for series and parallel inductors, RL time constants, and impedance.
Inductor Calculator answers four related circuit questions: the equivalent inductance of series or parallel parts, the time constant of a first-order RL circuit, and an ideal inductor's impedance at a chosen frequency. Enter inductance values with the intended unit, plus resistance or frequency where the calculation needs it. The easy-to-miss point is that the parallel formula assumes uncoupled inductors. Coils that share magnetic flux can produce a different result, so the basic calculation does not cover transformer windings or deliberately coupled coils.
A concrete input and expected output from the current implementation.
Input
Calculation: series L1: 10 mH L2: 20 mH
Expected output
Equivalent inductance: 30 mH
Series inductances add directly. Therefore, 10 mH + 20 mH = 30 mH, which is also 0.030 H.
For inductors in series, the calculator adds the entered inductances: L_eq = L1 + L2 + .... For uncoupled inductors in parallel, it adds their reciprocals and inverts the sum: 1/L_eq = 1/L1 + 1/L2 + .... Two parallel values can also be checked with L1L2/(L1+L2). Unit prefixes must be interpreted consistently.
The RL calculation uses tau = L/R, where tau is in seconds when L is in henries and R is in ohms. For an ideal inductor, Z_L = j 2 pi f L, with magnitude X_L = 2 pi f L ohms. Inductive reactance therefore increases in direct proportion to both frequency and inductance.
Not reliably unless their magnetic coupling has already been accounted for. The ordinary series and parallel equations assume zero mutual inductance. Coupled coils require a mutual-inductance term, and its sign depends on winding orientation. Treat transformer windings, common-mode chokes, and other coils sharing substantial magnetic flux as a coupled-inductor problem.
Use the total resistance in the inductor's charging or discharge path, not automatically the labeled value of one resistor. This may include source resistance and the coil's winding resistance. In the ideal first-order result, after one time constant current has risen to about 63.2 percent of its final value, or decayed to about 36.8 percent.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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