Capacitive Reactance Calculator
Find capacitor reactance in an AC circuit from frequency and capacitance.
Introduction
The capacitive reactance calculator helps estimate how much a capacitor opposes alternating current at a given frequency. This is a common calculation in AC circuit design, electronics, filter networks, audio coupling, timing circuits, and general power analysis. Engineers, technicians, and students use capacitive reactance when they need to understand how a capacitor behaves in a real AC system instead of looking only at the capacitance value printed on the component body.
Capacitive reactance falls as frequency increases and also falls as capacitance increases. That simple relationship explains why small capacitors can strongly limit low-frequency current while larger capacitors can pass more AC current at the same frequency. This page gives a quick answer and also shows the formula, units, and worked examples so the result is easier to apply in practical engineering work.
This makes the calculator useful for filter design, coupling networks, AC analysis, and quick comparisons between capacitor values before selecting real components for a circuit.
Formula
Xc = 1 / (2 x pi x f x C)
This is the standard formula for the reactance of an ideal capacitor in a sinusoidal AC circuit.
Variable Definitions
Xc = capacitive reactance in Ohm
f = frequency in hertz
C = capacitance in farads
pi = 3.14159
Units
Frequency is entered in hertz. Capacitance can be entered in farads, millifarads, microfarads, nanofarads, or picofarads. The calculator converts the selected unit to farads before applying the equation. The result is then displayed in Ohm, kOhm, or MOhm depending on the reactance level.
Worked Example 1
Suppose a capacitor has a value of 10 uF and the supply frequency is 50 Hz.
Xc = 1 / (2 x pi x 50 x 10 x 10^-6)
Xc is approximately 318.31 Ohm.
This means the capacitor presents about 318 Ohm of opposition to AC at 50 Hz.
Worked Example 2
Consider a 100 nF capacitor used in an electronic circuit at 1 kHz.
Xc = 1 / (2 x pi x 1000 x 100 x 10^-9)
Xc is approximately 1591.55 Ohm, or about 1.59 kOhm.
The smaller capacitance produces a larger reactance at the same order of frequency.
Practical Notes
Capacitive reactance is useful when selecting filter parts, coupling capacitors, timing components, and capacitor banks for AC applications. The equation assumes an ideal capacitor. In real circuits, tolerance, equivalent series resistance, leakage, voltage rating, and temperature can all influence final behavior. Use this calculator for quick design checks, then confirm the final component choice with the larger circuit and the component data sheet.