Inductive and Capacitive Reactance Calculator
Choose an inductor or a capacitor, then enter the frequency and the value. You get the reactance in ohms, and the impedance and phase if you add a resistor in series.
Worked examples
Inductor
10 mH at 1 kHz
62.83 ohms
2 x pi x 1000 x 0.01.
Capacitor
100 uF at 50 Hz
31.83 ohms
1 / (2 x pi x 50 x 0.0001).
About Inductive and Capacitive Reactance Calculator
Inductors and capacitors oppose alternating current in different ways. Inductive reactance rises with frequency, so a coil passes low frequencies easily and blocks high ones. Capacitive reactance falls with frequency, so a capacitor blocks direct current and passes high frequencies. This calculator gives the reactance of either in ohms from the frequency and the component value.
Reactance is not the same as resistance, because it does not turn power into heat. When there is a resistor in series, the two combine at right angles, and the page gives the impedance, the phase angle and the power factor. In an inductor the voltage leads the current and in a capacitor it lags, and the angle tells you by how much. Enter a voltage to see the current that would flow through the part.
How to use Inductive and Capacitive Reactance Calculator
- Choose an inductor or a capacitor.
- Enter the frequency and the inductance or capacitance, choosing the unit.
- Optionally enter a series resistance to get the impedance and phase angle.
- Optionally enter a voltage to see the current.
Common uses
- Checking a capacitor used to drop mains voltage
- Designing filters, chokes and tone controls
- Working out the impedance of a speaker crossover part
- Physics and electronics coursework on AC circuits
Frequently asked questions
What is the formula for inductive reactance?
XL = 2 x pi x f x L, with frequency in hertz and inductance in henries. A 10 millihenry coil at 1 kilohertz has a reactance of 62.8 ohms.
What is the formula for capacitive reactance?
XC = 1 / (2 x pi x f x C). A 100 microfarad capacitor at 50 hertz has a reactance of 31.8 ohms.
Is reactance the same as impedance?
No. Impedance is the total opposition to AC, combining resistance and reactance at right angles. Reactance alone describes only the inductor or capacitor.
Why does a capacitor block DC?
At zero frequency the capacitive reactance is infinite, so no steady current flows once the capacitor is charged. An inductor does the opposite and passes DC freely.