Capacitive Reactance Calculator
Enter a capacitance and frequency to instantly calculate capacitive reactance (Xc). Results are shown in Ω, kΩ, and MΩ — whichever is most readable for the value.
Results update as you type.
How to Use This Capacitive Reactance Calculator
Enter your capacitor value and select its unit from the dropdown (F, mF, µF, nF, or pF). Then enter the signal frequency and choose its unit (Hz, kHz, or MHz). The capacitive reactance is calculated instantly and displayed in ohms, kilohms, and megohms.
Capacitive reactance tells you how much a capacitor opposes AC current at a given frequency. A large reactance means the capacitor blocks most of the current; a small reactance means it passes it easily.
Capacitive Reactance Formula
Capacitive reactance is calculated using:
Where:
- Xc — Capacitive reactance (ohms, Ω)
- π — Pi ≈ 3.14159
- f — Frequency in hertz (Hz)
- C — Capacitance in farads (F)
Both frequency and capacitance appear in the denominator, so increasing either one will decrease the reactance — the capacitor becomes a lower impedance to current flow as frequency or capacitance rises.
Example
Given: C = 100 nF, f = 1 kHz
Step 1 — Convert units:
C = 100 nF = 100 × 10−9 F = 0.0000001 F
f = 1 kHz = 1000 Hz
Step 2 — Apply the formula:
Xc = 1 / (2 × 3.14159 × 1000 × 0.0000001)
Step 3 — Evaluate the denominator:
= 1 / 0.0006283
Result:
Xc ≈ 1591.5 Ω ≈ 1.59 kΩ
Frequently Asked Questions
What is capacitive reactance?
Capacitive reactance (Xc) is the opposition a capacitor presents to alternating current. Unlike resistance, it is frequency-dependent: it decreases as frequency increases, so a capacitor acts like an open circuit at DC (0 Hz) and a near short-circuit at very high frequencies.
What units is capacitive reactance measured in?
Capacitive reactance is measured in ohms (Ω), the same unit as resistance. It can be expressed in kilohms (kΩ) or megohms (MΩ) for convenience when the value is large.
Why does reactance decrease when frequency increases?
Because frequency appears in the denominator of the formula Xc = 1/(2πfC). As the signal switches polarity more rapidly, the capacitor has less time to charge and therefore opposes the current less strongly.
What is the difference between reactance and impedance?
Reactance is the purely reactive (energy-storing) part of impedance. Impedance also includes resistance. In a circuit with only a capacitor, the impedance equals the reactance. In a real RC circuit the impedance combines both R and Xc.
What is considered a high or low reactance?
This depends on the circuit context. As a rough guide: Xc above 1 MΩ is very high (the capacitor is essentially open); below 1 Ω is very low (near short-circuit at that frequency). Values in between indicate partial attenuation.