Calculate Capacitive Reactance
Enter frequency and capacitance to find XC.
What Is Capacitive Reactance?
Capacitive reactance is the opposition that a capacitor presents to alternating current. It is represented by the symbol XC and is measured in ohms (Ω), just like resistance.
Unlike ordinary resistance, capacitive reactance changes with frequency. A higher AC frequency or a larger capacitance produces a lower capacitive reactance.
Capacitive Reactance Formula
The capacitive reactance of an ideal capacitor can be calculated using frequency and capacitance.
In this equation, XC is capacitive reactance in ohms, f is frequency in hertz, C is capacitance in farads, and π is approximately 3.14159.
How to Use the Capacitive Reactance Calculator
- Enter the AC frequency.
- Select Hz, kHz, MHz, or GHz.
- Enter the capacitance value.
- Choose pF, nF, µF, mF, or F.
- Click Calculate Reactance.
- The result will be displayed automatically in Ω, kΩ, or MΩ.
The calculator converts frequency to hertz and capacitance to farads internally before applying the capacitive reactance formula.
Capacitive Reactance Example
Suppose a 0.1 µF capacitor is used in an AC circuit operating at 1 kHz. First convert the values to base SI units.
C = 0.1 µF = 0.0000001 F
XC = 1 / (2 × π × 1000 × 0.0000001)
XC ≈ 1.59 kΩ
This means the capacitor presents approximately 1.59 kilo-ohms of reactance at a frequency of 1 kHz.
How Frequency Affects Capacitive Reactance
Higher Frequency
When frequency increases, capacitive reactance decreases. The capacitor allows higher-frequency AC signals to pass more easily.
Lower Frequency
When frequency decreases, capacitive reactance increases, so the capacitor provides more opposition to current.
DC Condition
At ideal steady-state DC, frequency is zero and capacitive reactance approaches an extremely large value.
How Capacitance Affects Reactance
Capacitance and capacitive reactance have an inverse relationship. Increasing capacitance reduces XC when frequency remains constant.
For example, doubling the capacitance at the same frequency cuts the capacitive reactance in half. This relationship is important when selecting capacitors for filters, coupling circuits, and frequency-dependent networks.
Frequency and Capacitance Units
| Quantity | Unit | Conversion |
|---|---|---|
| Frequency | Hz | 1 Hz |
| Frequency | kHz | 1,000 Hz |
| Frequency | MHz | 1,000,000 Hz |
| Frequency | GHz | 1,000,000,000 Hz |
| Capacitance | pF | 10-12 F |
| Capacitance | nF | 10-9 F |
| Capacitance | µF | 10-6 F |
| Capacitance | mF | 10-3 F |
Where Is Capacitive Reactance Used?
Filters
Reactance calculations help determine how capacitors behave in low-pass, high-pass, and other frequency-selective circuits.
Audio Circuits
Capacitors are widely used for coupling, filtering, and frequency control in audio electronics.
Electronic Design
Engineers use XC when selecting capacitors for AC circuits, signal processing, oscillators, and power electronics.
Frequently Asked Questions
What is capacitive reactance?
Capacitive reactance is the opposition a capacitor provides to alternating current. It is measured in ohms and varies with both frequency and capacitance.
What is the formula for capacitive reactance?
The formula is XC = 1 / (2πfC), where f is frequency in hertz and C is capacitance in farads.
Does capacitive reactance decrease with frequency?
Yes. As frequency increases, capacitive reactance decreases. This is why capacitors offer less opposition to higher-frequency AC signals.
What happens to capacitive reactance when capacitance increases?
Capacitive reactance decreases as capacitance increases, assuming the frequency remains unchanged.
What unit is capacitive reactance measured in?
Capacitive reactance is measured in ohms (Ω). Larger results may also be expressed in kilo-ohms or mega-ohms.
Can I use kHz and µF directly in this calculator?
Yes. The calculator supports common frequency and capacitance units and automatically converts them before performing the calculation.