Enter the nominal capacitance.
Enter the operating frequency.
Real Capacitor Parameters
Add ESR and ESL to calculate the impedance of a practical capacitor. Set either value to 0 if it is not available.
Series resistance of the capacitor.
Parasitic inductance of the capacitor.
Calculation Result
Calculation Formula
Quick Examples
Capacitor Impedance vs. Frequency
The chart shows how capacitor impedance changes with frequency. For a real capacitor, ESL can cause the impedance to reach a minimum at the self-resonant frequency and increase again at higher frequencies.
Impedance at Different Frequencies
Compare capacitor impedance across frequencies. For a real capacitor, the table automatically includes the self-resonant frequency and the selected operating frequency.
| Frequency | XC | XL | |Z| | Phase | Behavior |
|---|
How Capacitor Impedance Works
A real capacitor does not behave like a perfectly ideal capacitor, especially at high frequencies. Its impedance is affected by capacitance, ESR and parasitic inductance.
What Is Capacitor Impedance?
Capacitor impedance describes the total opposition that a capacitor presents to alternating current at a specific frequency.
For an ideal capacitor, impedance is determined entirely by capacitive reactance.
For a real capacitor, ESR and ESL also affect the total impedance.
Capacitive Reactance
The capacitive reactance of an ideal capacitor is:
XC = 1 / (2πfC)
- Higher frequency → Lower XC
- Higher capacitance → Lower XC
- Lower frequency → Higher XC
What Is ESR?
ESR means Equivalent Series Resistance. It represents resistive losses inside a practical capacitor.
ESR contributes directly to the impedance magnitude and determines the minimum impedance in the simplified series RLC model.
What Is ESL?
ESL means Equivalent Series Inductance. It represents parasitic inductance caused by capacitor construction and electrical connections.
At sufficiently high frequencies, ESL can dominate capacitor behavior.
Self-Resonant Frequency
The self-resonant frequency occurs when capacitive and inductive reactance are equal.
At resonance:
XC = XL
In the simplified series model, impedance reaches its minimum near this frequency.
Series RLC Model
For a practical capacitor:
Z = ESR + j(XL − XC)
The impedance magnitude is:
|Z| = √[ESR² + (XL − XC)²]
Engineering Note: Why High-Frequency Impedance Matters
For high-frequency filtering and EMI suppression applications, nominal capacitance alone does not determine performance. ESR, ESL, mounting configuration, lead length and internal construction can significantly influence the actual impedance characteristics of a capacitor.
Capacitor Impedance in EMI Filtering
Low impedance at unwanted frequencies is often an important requirement for effective noise suppression and filtering.
EMI Noise Bypass
A capacitor can provide a low-impedance path for unwanted high-frequency noise.
Feedthrough Capacitors
Feedthrough capacitors are designed to provide effective high-frequency filtering by creating a low-impedance path through an enclosure boundary.
Frequency-Dependent Performance
The impedance of a capacitor changes with frequency, so component selection should consider the actual operating frequency range.
Parasitic Inductance
Reducing connection length and parasitic inductance can improve high-frequency filtering performance.
Mounting Effects
The capacitor mounting method and connection geometry can add additional parasitic inductance that is not included in a simple component-level model.
Model Limitations
Actual capacitor impedance depends on construction and frequency. For precise design work, manufacturer impedance or S-parameter data should be used when available.