Reactance Calculator

A reactance calculator determines the opposition created by inductors and capacitors in an AC circuit. The result is expressed in ohms and is used as an input to impedance, resonance, current, voltage-drop, power-factor, filter, and motor-control calculations.

Unlike resistance, reactance changes with frequency. An inductor produces inductive reactance that increases as frequency rises. A capacitor produces capacitive reactance that decreases as frequency rises. When both components are present, their values offset each other algebraically to produce a net reactance.

This worksheet supplies reactance values to the canonical impedance and resonance workflows.

Inputs and Results

Enter the operating conditions using the calculator’s actual fields:

Field	Electrical meaning
Frequency	Operating frequency in hertz (Hz)
Inductance	Circuit inductance in millihenries (mH)
Capacitance	Circuit capacitance in microfarads (uF)

The calculator returns:

Result	Electrical meaning
Inductive reactance	The inductor’s AC opposition, \(X_L\), in ohms
Capacitive reactance	The capacitor’s AC opposition, \(X_C\), in ohms
Net reactance	The algebraic difference between inductive and capacitive reactance
Reactance type	Whether the net circuit behavior is inductive, capacitive, or balanced at resonance

A positive net reactance is inductive. A negative net reactance is capacitive. A net reactance of zero indicates ideal series resonance at the entered frequency.

Reactance Formula

The calculator converts the entered component units before applying standard AC reactance equations.

\(X_L = 2\pi fL\)

\(X_C = \frac{1}{2\pi fC}\)

\(\displaystyle X = X_L - X_C\)

Where:

• \(X_L\) = inductive reactance in ohms
• \(X_C\) = capacitive reactance in ohms
• (X) = net reactance in ohms
• (f) = frequency in hertz
• (L) = inductance in henries
• (C) = capacitance in farads

For the calculator inputs:

\(\displaystyle L_{\text{H}} = \frac{L_{\text{mH}}}{1{,}000}\)

\(\displaystyle C_{\text{F}} = \frac{C_{\text{uF}}}{1{,}000{,}000}\)

The result is pure reactance arithmetic. It does not calculate resistance, total impedance magnitude, current, real power, apparent power, conductor ampacity, or voltage drop by itself.

Calculation Example

Using the entered values:

• Frequency: 60 Hz
• Inductance: 10 mH
• Capacitance: 10 uF

Convert the component values:

\(\displaystyle 10\text{ mH} = 0.010\text{ H}\)

\(\displaystyle 10\text{ uF} = 0.000010\text{ F}\)

Calculate inductive reactance:

\(\displaystyle X_L = 2\pi(60)(0.010)\)

\(\displaystyle X_L = 3.7699 \Omega\)

Calculate capacitive reactance:

\(\displaystyle X_C = \frac{1}{2\pi(60)(0.000010)}\)

\(\displaystyle X_C = 265.2582 \Omega\)

Calculate net reactance:

\(\displaystyle X = 3.7699 - 265.2582\)

\(\displaystyle \mathbf{X = -261.4883 Omega}\)

The calculator reports:

Result	Value
Inductive reactance	3.7699 ohm
Capacitive reactance	265.2582 ohm
Net reactance	-261.4883 ohm
Reactance type	capacitive

The negative net result means the capacitive reactance is larger than the inductive reactance at 60 Hz. In a series AC calculation, the circuit has capacitive reactance and current leads voltage, subject to the rest of the circuit impedance.

Impedance and Resonance Use

Reactance is one part of AC impedance. For a series circuit with resistance (R), the impedance magnitude is:

\(\displaystyle Z = \sqrt{R^2 + X^2}\)

The net reactance from this worksheet is used with circuit resistance when determining total impedance and prospective AC current:

\(\displaystyle I = \frac{V}{Z}\)

When inductive and capacitive reactance are equal:

\(\displaystyle X_L = X_C\)

\(\displaystyle X = 0\)

That condition is series resonance. At ideal resonance, the reactive portions cancel and the remaining impedance is primarily resistance. Real equipment still has conductor resistance, coil losses, capacitor losses, harmonic content, component tolerances, and frequency-dependent behavior.

Typical electrical applications include:

• Reviewing the effect of capacitors on inductive loads and power-factor correction systems.
• Checking L-C filter behavior at a specified operating frequency.
• Establishing values for impedance and resonance calculations.
• Evaluating circuit response in controls, drives, transformers, relay coils, and electronic power equipment.
• Estimating reactive opposition before calculating current or voltage drop in an AC circuit with known resistance and supply voltage.

Field Verification

The calculated value assumes ideal inductance and capacitance at the entered Frequency. Actual component behavior can differ because of tolerance, temperature, core characteristics, equivalent series resistance, parasitic inductance, dielectric losses, saturation, harmonics, and non-sinusoidal waveforms.

Do not use net reactance alone to select branch-circuit conductors, feeder conductors, AWG or kcmil sizes, overcurrent protection, raceway fill, or equipment ratings. Those decisions require the complete circuit conditions, including voltage, load type, continuous-load treatment where applicable, conductor ampacity, insulation temperature rating, terminal rating, adjustment factor, correction factor, current-carrying conductors, installation method, and AHJ requirements.

Verify capacitor voltage rating, inductor current rating, insulation system, fault duty, switching transients, and manufacturer limits separately.