Impedance & Reactance Calculator
Capacitive and inductive reactance, total impedance and phase angle at a given frequency.
Example: At 1 kHz this series network has an impedance of 188 Ω at -57.9°.
Formula
X_C = 1 / (2πfC) X_L = 2πfL |Z| = √(R² + (X_L − X_C)²)Worked example
At 1 kHz this series network has an impedance of 188 Ω at -57.9°.
X_C = 1 / (2πfC)
1 / (2π × 1 kHz × 1 µF)
159.2 Ω
Capacitive reactance falls as frequency rises — a capacitor is an open circuit at DC.
|Z| = √(R² + (X_L − X_C)²)
√((100 Ω)² + (-159.2 Ω)²)
188 Ω
Frequently asked questions
What is capacitive reactance?
A capacitor's opposition to AC, X_C = 1/(2πfC), in ohms. It falls as frequency rises: a 1 µF capacitor is about 159 Ω at 1 kHz but only 1.59 Ω at 100 kHz. At DC it is infinite, which is why capacitors block DC.
How is impedance different from resistance?
Resistance dissipates energy and does not depend on frequency. Reactance stores and returns it, shifting the phase between voltage and current, and does depend on frequency. Impedance is the two combined as a complex quantity — magnitude plus phase.
Why do inductive and capacitive reactance subtract?
Because they shift phase in opposite directions — an inductor's current lags, a capacitor's leads. At the frequency where they are equal they cancel completely, which is what resonance is.
What does the phase angle tell me?
How far the current leads or lags the voltage. Positive means inductive, with current lagging; negative means capacitive, with current leading; zero means the circuit looks purely resistive at that frequency, whatever it contains.
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