Capacitive Reactance Calculator
This capacitive reactance calculator finds how much a capacitor opposes alternating current at a given frequency, using Xc = 1 / (2π f C). Enter the frequency and the capacitance, and the capacitive reactance calculator returns the reactance in ohms and kilohms. It is a quick way to calculate Xc of a capacitor for filters and AC circuits.
Results
The Capacitive Reactance Calculator is part of our Electronics collection. Browse more electronics to size, convert, and check your work alongside this tool.
What the capacitive reactance calculator shows
A capacitor blocks direct current but passes alternating current, and the higher the frequency, the more easily it passes. The capacitive reactance calculator gives that opposition, Xc, in ohms. As a reactance capacitor calculator it helps you choose capacitors for filters, coupling, and power factor correction.
Capacitive reactance formula calculator
The capacitive reactance formula calculator uses:
f is the frequency in hertz and C the capacitance in farads. Reactance falls as frequency or capacitance rises, so a capacitor looks like an open circuit at DC and close to a short circuit at very high frequency.
Capacitor Xc calculator example
A 10 µF capacitor at 60 Hz. The capacitor xc calculator gives:
At 6 kHz the same capacitor drops to about 2.65 Ω, a hundred times lower.
How to calculate xc capacitor values
To calculate Xc of a capacitor, enter the frequency in hertz and the capacitance in microfarads. The capacitive reactance calculator returns the reactance in ohms and kilohms. For mains work use 50 or 60 Hz; for audio and radio circuits use the signal frequency.
Reading the capacitive reactance calculator result
Reactance behaves like resistance for limiting AC current, but it stores and returns energy instead of turning it into heat. Current through a capacitor leads the voltage by 90 degrees. Combine Xc with resistance as an impedance, Z = √(R² + Xc²), when both are in series.
When to use the xc capacitor calculator
- Designing RC filters with the xc capacitor calculator
- Choosing coupling and bypass capacitors
- Sizing capacitors for power factor correction
- Checking capacitor current at mains frequency
Common capacitive reactance calculator mistakes
- Microfarads as farads. 10 µF is 0.00001 F.
- Forgetting 2π. Angular frequency is 2πf.
- Adding Xc to R directly. Combine them as √(R² + Xc²).
Tips for accurate results
- Use the actual circuit frequency.
- Allow for capacitor tolerance, often ±10 to 20 percent.
- Check voltage ratings for AC use.
Calculate Xc capacitor values for filters
In a simple RC low-pass filter, the cutoff frequency is where Xc equals R. To calculate Xc capacitor values for a filter, pick the cutoff, set Xc equal to the resistor, and solve for C. A 1 kΩ resistor with a 159 nF capacitor gives a cutoff near 1 kHz. Capacitors also store energy, which the capacitor energy calculator works out from capacitance and voltage.
Capacitive reactance calculator vs impedance
Real capacitors have a little series resistance and inductance, so at high frequency their impedance stops falling. The capacitive reactance calculator gives the ideal value; for RF work, check the capacitor's datasheet impedance curve.
Capacitive reactance calculator reference at 60 Hz
| Capacitance | XC at 60 Hz | XC at 50 Hz |
|---|---|---|
| 1 µF | 2,653 Ω | 3,183 Ω |
| 10 µF | 265 Ω | 318 Ω |
| 47 µF | 56 Ω | 68 Ω |
| 100 µF | 26.5 Ω | 31.8 Ω |
Capacitive Reactance Calculator FAQ
What is the capacitive reactance formula?
Xc = 1 / (2πfC), with f in hertz and C in farads.
Why does reactance fall with frequency?
A capacitor charges and discharges more often at higher frequency, so more current flows for the same voltage.
Is capacitive reactance the same as resistance?
Both are in ohms, but reactance stores energy and shifts the phase, while resistance turns energy into heat.
What is Xc at DC?
Infinite, in theory, since frequency is zero. A capacitor blocks steady DC once charged.