Reactance Calculator | XL = 2πfL & XC = 1/(2πfC)
Calculate inductive reactance XL=2πfL and capacitive reactance XC=1/(2πfC). Input frequency and component value to find AC resistance.
Inductive Reactance (XL)
Capacitive Reactance (XC)
How to Use
- Enter the signal frequency with unit (Hz, kHz, or MHz).
- For inductive reactance: enter the inductance value (nH, µH, or mH) and click 'Calculate XL'.
- For capacitive reactance: enter the capacitance value (pF, nF, or µF) and click 'Calculate XC'.
- Results show XL = 2πfL or XC = 1/(2πfC) in ohms.
- You can calculate both at the same time if you enter all three values.
- Use these results in the Impedance Calculator to find total Z and phase angle.
About Reactance
Inductive Reactance
Inductive reactance XL = 2πfL (in ohms) represents the opposition of an inductor to AC current. It increases linearly with frequency: at higher frequencies, the inductor changes current more rapidly, inducing a larger back-EMF that opposes the current. At DC (f=0), XL=0 — the inductor is a short circuit. At very high frequencies, XL becomes large — the inductor blocks high-frequency signals. This is the basis of high-pass and bandpass filters.
Capacitive Reactance
Capacitive reactance XC = 1/(2πfC) (in ohms) represents the opposition of a capacitor to AC current. It decreases with increasing frequency: at higher frequencies, the capacitor charges and discharges more rapidly, allowing more current. At DC (f=0), XC = ∞ — the capacitor is an open circuit. At very high frequencies, XC approaches zero — the capacitor is nearly a short circuit. This frequency-dependent behavior enables filtering and impedance matching.
Reactance vs. Resistance
Resistance dissipates energy as heat and is frequency-independent. Reactance stores energy (inductors in magnetic fields, capacitors in electric fields) and is frequency-dependent. While resistance always opposes current, reactance either opposes (in phase opposition) or assists current flow depending on the phase relationship. In complex impedance notation: Z = R + jXL − jXC, where j indicates the imaginary (reactive) component.
Frequency Response Design
Understanding reactance at different frequencies is key to filter design. An RC low-pass filter has XC = R at the cutoff frequency: f_c = 1/(2πRC). An RL high-pass filter has XL = R at cutoff: f_c = R/(2πL). Combining reactances (LC circuits) creates sharper filter responses. Audio equalizers, speaker crossovers, RF amplifiers, and switching power supply filters all rely on carefully calculated reactances.
Key Features
- Calculates XL = 2πfL and XC = 1/(2πfC) simultaneously
- Flexible unit selection: Hz/kHz/MHz, nH/µH/mH, pF/nF/µF
- Shows angular frequency ω = 2πf
- Results feed directly into impedance and filter calculations
Common Applications
- Filter cutoff frequency verification
- RF circuit impedance analysis
- Audio crossover component selection
- Switching power supply inductor and capacitor sizing
- AC circuit analysis for education and design