Capacitance Value
Frequency
| Capacitance | @ 60 Hz | @ 1 kHz | @ 1 MHz |
|---|---|---|---|
| 10 pF | 265 MΩ | 15.9 MΩ | 15.9 kΩ |
| 100 pF | 26.5 MΩ | 1.59 MΩ | 1.59 kΩ |
| 1 nF | 2.65 MΩ | 159 kΩ | 159 Ω |
| 10 nF | 265 kΩ | 15.9 kΩ | 15.9 Ω |
| 100 nF | 26.5 kΩ | 1.59 kΩ | 1.59 Ω |
| 1 µF | 2.65 kΩ | 159 Ω | 0.16 Ω |
| 10 µF | 265 Ω | 15.9 Ω | 0.016 Ω |
| 100 µF | 26.5 Ω | 1.59 Ω | 1.6 mΩ |
Capacitor Impedance Calculator: Find Reactance at Any Frequency
Last month I was debugging an audio filter that hummed at 60 Hz, and the culprit was a capacitor whose impedance I had badly underestimated. A 1 µF cap behaves like an open circuit at DC but nearly a short at 1 MHz—and that single number decides whether your design works.
What Capacitor Impedance Is and Why It Matters
Capacitor impedance is the frequency-dependent opposition a capacitor presents to AC current. Unlike a resistor’s fixed ohms, a capacitor’s impedance falls as frequency rises. Engineers use the term reactance (Xc)—the imaginary, energy-storing part of impedance that doesn’t dissipate heat. Getting this right matters for filters, decoupling networks, power supplies, and EMI suppression. Pick the wrong capacitance and your filter cutoff shifts, your supply rail rings, or noise leaks straight through. This is why every datasheet plots impedance versus frequency rather than a single value.
How to Calculate Capacitor Impedance
For an ideal capacitor, the reactance formula is:
Xc = 1 / (2 × π × f × C)
where f = frequency (Hz), C = capacitance (Farads)
Example: Take a 10 µF (0.00001 F) capacitor at 1 kHz.
Xc = 1 / (2 × 3.1416 × 1000 × 0.00001) = 1 / 0.0628 ≈ 15.9 Ω.
Push frequency to 100 kHz and Xc drops to just 0.159 Ω—a 100× decrease for a 100× frequency increase. That inverse relationship is the core of capacitor behavior, and our calculator above runs it instantly for any C and f.
The ESR Trap Most Beginners Miss
Here’s a common misconception: that impedance keeps dropping forever as frequency rises. It doesn’t. Real capacitors have ESR (equivalent series resistance) and ESL (parasitic inductance). In my bench testing, a 10 µF electrolytic hit a minimum impedance around 100 kHz, then climbed again as ESL took over—it started acting like an inductor. The lowest point is the self-resonant frequency (SRF). The IEC 60384 standard for fixed capacitors defines how these parasitics are characterized and measured. Material matters too: ceramic MLCCs often show ESR near 5–20 mΩ, while aluminum electrolytics can sit at 100 mΩ to several ohms—a 10–100× difference that decides which cap you trust for high-frequency decoupling.
Pro Tips
✅ Always check the datasheet impedance curve, not just nominal capacitance—the SRF tells you the usable frequency range.
✅ Parallel a small ceramic (100 nF) with a bulk electrolytic to cover both low and high frequencies effectively.
✅ For decoupling, target the impedance minimum near your switching frequency; verify with an LCR meter rather than trusting math alone.
Conclusion
Capacitor impedance changes dramatically with frequency, and ESR/ESL reshape the curve at high frequencies. Enter your capacitance and frequency in the calculator above to get instant, accurate reactance values for your next design.
Frequently Asked Questions
What is the formula for capacitor impedance?
The ideal reactance is Xc = 1 / (2πfC), where f is frequency in Hz and C is capacitance in Farads. The result is in ohms.
Does capacitor impedance increase or decrease with frequency?
Ideal capacitor impedance decreases as frequency rises. In real capacitors, it bottoms out at the self-resonant frequency, then rises due to parasitic inductance.
Why does my capacitor impedance go up at high frequencies?
Above the self-resonant frequency, parasitic inductance (ESL) dominates, so the capacitor behaves like an inductor and impedance climbs again.
Is capacitive reactance the same as impedance?
Not exactly. Reactance (Xc) is the ideal reactive part. Full impedance also includes ESR, making it a complex value, not just reactance.
Can I use this calculator for electrolytic capacitors?
Yes, for ideal reactance. But electrolytics have higher ESR, so check the datasheet impedance curve for accurate real-world values.
Last Updated on June 21, 2026 by Kevin Chen
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