Calculate inductive reactance X_L = 2πfL, impedance, phase angle, and Q factor. Frequency response table shows how inductors behave across frequencies.
Inductive reactance is the opposition an inductor presents to alternating current, and it increases linearly with frequency. The formula X_L = 2πfL shows that an inductor that passes DC freely becomes increasingly resistive to higher-frequency AC signals — the fundamental principle behind inductive filters, chokes, and impedance matching networks.
This calculator computes inductive reactance, total impedance (with series resistance), phase angle, current, power factor, quality factor (Q), and the L/R time constant. It shows how all these quantities change across a range of frequencies, making it invaluable for circuit design and analysis.
Whether you are designing a power supply filter, analyzing an RL circuit for a physics class, selecting an inductor for an RF application, or calculating the impedance of a motor winding, this calculator provides all the key parameters. The frequency response table and power analysis give complete insight into the inductor's AC behavior. Check the example with realistic values before reporting.
AC circuit analysis with inductors requires combining reactance and resistance as complex numbers to find impedance, then deriving phase angle, power factor, and current. This calculator does it all in one step, plus shows the frequency-dependent behavior that is central to filter and circuit design. The Q factor output is especially useful for resonant circuit design.
Inductive Reactance: X_L = 2πfL Impedance (RL series): Z = √(R² + X_L²) Phase Angle: φ = arctan(X_L / R) Quality Factor: Q = X_L / R = 2πfL / R Time Constant: τ = L / R Where: f = frequency (Hz) L = inductance (H) R = resistance (Ω)
Result: X_L = 3.77 Ω, Z = 50.14 Ω
A 10 mH inductor at 60 Hz: X_L = 2π × 60 × 0.01 = 3.77 Ω. With 50 Ω resistance, Z = √(50² + 3.77²) = 50.14 Ω. The phase angle is arctan(3.77/50) = 4.3°, nearly resistive. At 120V, the current is 2.39 A.
When AC voltage is applied to an inductor, the current lags the voltage by up to 90°. This phase relationship is the basis of inductive reactance. In a pure inductor (no resistance), all energy is stored in the magnetic field during one quarter cycle and returned to the circuit during the next. Adding resistance creates a complex impedance that determines both the magnitude and phase of the current.
Inductors combined with capacitors and resistors form the building blocks of signal filters. A series inductor blocks high-frequency signals (low-pass behavior) because X_L increases with frequency. This principle is used in power supply filtering, EMI suppression, audio crossover networks, and RF front-end circuits. The Q factor determines the sharpness of the filter's frequency response.
In switch-mode power supplies, the inductor must handle both DC bias current and AC ripple. The inductance value determines ripple current magnitude, while the core material and wire gauge determine losses at the switching frequency (typically 50 kHz to 2 MHz). This calculator helps evaluate whether a candidate inductor provides sufficient impedance at the switching frequency.
Inductive reactance (X_L) is the opposition an inductor provides to AC current. It increases with frequency: X_L = 2πfL. Unlike resistance, reactance does not dissipate energy — it stores and returns energy to the circuit each cycle.
Higher frequency means the current changes direction more rapidly. The inductor's back-EMF (which opposes current change) is proportional to the rate of change, so faster changes produce stronger opposition.
Reactance (X_L) is only the inductor's opposition. Impedance (Z) combines both resistance and reactance: Z = √(R² + X_L²). Impedance is what actually determines the current in a real circuit.
Q = X_L/R measures how "ideal" an inductor is. High Q (>100) means the inductor has very low losses relative to its reactance — desirable for resonant circuits and filters. Low Q means significant resistive losses.
Inductance is primarily determined by geometry and core material. Air-core inductors are very stable. Ferrite-core inductors can vary with temperature as the core permeability changes. Wire resistance also increases with temperature, reducing Q.
In an RL circuit, current lags voltage by the phase angle φ = arctan(X_L/R). At 0°, the circuit is purely resistive; at 90°, purely inductive. Most practical circuits fall between 10° and 60°.