Inductive Reactance Calculator
Calculate inductive reactance (XL) for a coil or inductor in an AC circuit at any frequency. Used in RF design, transformer analysis, and filter circuit development.
About this calculator
Inductive reactance (XL) is the opposition an inductor presents to alternating current, caused by the back-EMF generated as current changes. The formula is XL = 2π × f × L, where f is the frequency in hertz (Hz) and L is the inductance in henries (H). Since inductance is commonly specified in millihenries (mH), the calculator converts it: L(H) = L(mH) / 1,000, giving XL = 2 × π × f × (L_mH / 1,000). Reactance is expressed in ohms (Ω). Unlike capacitive reactance, inductive reactance increases with frequency — an inductor passes low-frequency currents easily and increasingly opposes high-frequency signals. This makes inductors fundamental building blocks for low-pass filters, chokes, and resonant LC circuits used in radio and power electronics.
How to use
Say you have a 50 mH inductor operating at 1000 Hz. Convert inductance to henries: 50 mH = 50 / 1,000 = 0.05 H. Apply the formula: XL = 2 × π × 1000 × 0.05 = 2 × 3.14159 × 1000 × 0.05 = 314.16 Ω. At 1000 Hz, the inductor presents approximately 314 Ω of reactance. Enter your frequency in Hz and inductance in mH into the calculator to get XL instantly for use in impedance calculations or filter design.
Frequently asked questions
What is inductive reactance and how is it different from resistance?
Inductive reactance (XL) is the frequency-dependent opposition an inductor offers to alternating current, measured in ohms. Resistance dissipates energy as heat and is constant regardless of frequency. Inductive reactance, by contrast, stores energy in a magnetic field and releases it back to the circuit, and its magnitude increases with frequency. Both affect current flow in a circuit, but only resistance causes real power loss; inductive reactance causes a phase shift between voltage and current.
How does frequency affect inductive reactance?
Inductive reactance is directly proportional to frequency: XL = 2π × f × L. Doubling the frequency doubles the reactance. At DC (0 Hz), XL is zero and the inductor acts like a plain wire. At very high frequencies, XL becomes large enough to effectively block AC signals. This is why inductors are used as chokes in power supplies — they pass DC while blocking high-frequency noise — and as low-pass filter elements in audio and RF circuits.
How do I calculate total impedance in a circuit with both inductive reactance and resistance?
When a resistor and inductor are in series, the total impedance Z is not simply R + XL because resistance and reactance are 90° out of phase. Instead, use the Pythagorean formula: Z = √(R² + XL²). For example, a 300 Ω resistor in series with an inductor showing 400 Ω of reactance gives Z = √(300² + 400²) = √(90000 + 160000) = √250000 = 500 Ω. This impedance value governs the current drawn from the source via Ohm's Law: I = V / Z.