Calculators
Reactance Calculator
Calculate capacitive reactance Xc = 1 / (2πfC) and inductive reactance Xl = 2πfL, or solve for frequency, capacitance, or inductance locally in your browser.
Use reactance formulas to relate frequency, reactance, capacitance, or inductance for AC circuits. Capacitive reactance is Xc = 1 ÷ (2 × π × f × C) and inductive reactance is Xl = 2 × π × f × L. Choose which quantity to solve for, enter the remaining positive values with matching unit families, and calculate. Reactance is the opposition a capacitor or inductor presents to alternating current, measured in ohms, and it changes with frequency. Calculations run locally in your browser; your values are not uploaded or stored.
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Relate reactance, frequency, capacitance, and inductance.
Reactance is the opposition that a capacitor or inductor presents to alternating current, measured in ohms, and it depends on frequency. Capacitive reactance is Xc = 1 ÷ (2 × π × f × C): capacitors block low frequencies and pass high frequencies. Inductive reactance is Xl = 2 × π × f × L: inductors pass low frequencies and block high frequencies. Enter frequency and a component value to find the reactance, or enter a target reactance with one value to solve for the other. For example, 1 kHz through 100 nF gives Xc ≈ 1.592 kΩ, and 100 Hz through a 100 mH inductor gives Xl ≈ 62.83 Ω. Capacitance and inductance accept pF to F and nH to H, and reactance and frequency are reported in automatically scaled units. The results assume ideal components with no resistance, tolerance error, parasitic capacitance or inductance, or core losses. All calculations run locally in your browser; your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
What is reactance?
Reactance is the opposition that a capacitor or inductor presents to alternating current, measured in ohms. Unlike resistance, reactance depends on frequency. Capacitive reactance decreases as frequency rises, while inductive reactance increases with frequency. Reactance alone does not dissipate power; it stores and releases energy each cycle.
How do I calculate capacitive reactance?
Capacitive reactance is Xc = 1 ÷ (2 × π × f × C), where f is the frequency in hertz and C is the capacitance in farads. For example, 1 kHz through 100 nF gives Xc = 1 ÷ (2 × π × 1000 × 0.0000001) ≈ 1.592 kΩ. A capacitor passes high frequencies more easily, so its reactance falls as frequency rises.
How do I calculate inductive reactance?
Inductive reactance is Xl = 2 × π × f × L, where f is the frequency in hertz and L is the inductance in henries. For example, 100 Hz through a 100 mH inductor gives Xl = 2 × π × 100 × 0.1 ≈ 62.83 Ω. An inductor passes low frequencies more easily, so its reactance rises as frequency rises.
How do I solve for frequency, capacitance, or inductance?
Rearrange the formulas. From capacitive reactance, frequency is f = 1 ÷ (2 × π × Xc × C) and capacitance is C = 1 ÷ (2 × π × f × Xc). From inductive reactance, frequency is f = Xl ÷ (2 × π × L) and inductance is L = Xl ÷ (2 × π × f). For example, a 1.592 kΩ reactance at 1 kHz implies a 100 nF capacitor.
Which units can I use?
Reactance accepts milliohms (mΩ), ohms (Ω), kilo-ohms (kΩ), and mega-ohms (MΩ); frequency accepts hertz (Hz), kilohertz (kHz), megahertz (MHz), and gigahertz (GHz); capacitance accepts picofarads (pF), nanofarads (nF), microfarads (µF), millifarads (mF), and farads (F); inductance accepts nanohenries (nH), microhenries (µH), millihenries (mH), and henries (H). Results are shown in automatically scaled units.
What are the limitations of this model?
The calculator assumes ideal components with no series resistance, tolerance error, parasitic capacitance or inductance, or core losses, and a sinusoidal steady-state signal. Real capacitors and inductors include equivalent series resistance and parasitics that shift behaviour, especially near self-resonance. It is an educational estimate for design intuition, not a substitute for measurement or simulation, and all calculations run locally in your browser.