What is capacitive reactance?

Capacitive reactance (Xc) is the opposition a capacitor offers to alternating current. Unlike resistance, it depends on frequency: Xc decreases as frequency rises, so a capacitor blocks low-frequency signals and passes high-frequency ones.

What is the formula used?

Xc = 1 / (2π × f × C), where f is frequency in hertz and C is capacitance in farads. The result is in ohms.

Why does reactance decrease at higher frequencies?

At higher frequencies the capacitor charges and discharges faster, so it opposes current less. The relationship is inversely proportional: doubling the frequency halves the reactance.

Is capacitive reactance the same as impedance?

For a pure (ideal) capacitor, the impedance magnitude equals Xc. In a real circuit with resistors or inductors, total impedance also includes resistance and inductive reactance combined as a complex vector.

What units should I enter?

Use the dropdowns to select the right prefix — for example 100 nF rather than 0.0000001 F. The calculator converts everything internally before computing.

Capacitive Reactance Calculator

Name: Capacitive Reactance Calculator
Availability: InStock
Author: Nham Vu

Enter a frequency and capacitance to instantly calculate capacitive reactance (Xc) in ohms using Xc = 1 / (2πfC).

Inputs

Frequency

Capacitance

Result

Enter values and click Calculate.

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Summary

Enter a frequency and capacitance to instantly calculate capacitive reactance (Xc) in ohms using Xc = 1 / (2πfC).

How it works

Enter the signal frequency and choose the unit (Hz, kHz, MHz, or GHz).
Enter the capacitance value and choose the unit (pF, nF, µF, mF, or F).
The calculator applies Xc = 1 / (2π × f × C) using full-precision arithmetic.
The result is displayed in ohms, with auto-scaling to kΩ or MΩ for readability.
The formula breakdown is shown so you can verify the substituted values.

Use cases

Design RC low-pass or high-pass filters for audio circuits.
Verify bypass capacitor behavior at a given switching frequency.
Determine the impedance of a coupling capacitor in an amplifier stage.
Check that a decoupling capacitor provides low impedance at the power-supply ripple frequency.
Quickly compare reactance across several capacitor values during PCB design.
Teach AC circuit theory: see how doubling frequency halves reactance.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu