Work out the reactance of a capacitor or inductor at any frequency, or solve backwards for the inductance, capacitance or frequency that gives a target reactance. Units from pF to F, nH to H and Hz to GHz are handled for you.
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Enter your values to see the result.
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How to use the Reactance Calculator
Choose what to calculate: X_L, X_C, L, C or frequency.
Enter the known values and pick their units (e.g. 100 nF, 1 kHz).
Read the result with automatic SI prefixes (Ω, kΩ, MΩ…).
Check the extras: complex impedance, susceptance and the component that would resonate with yours.
Use the chart and table to see how reactance changes with frequency.
Reactance formulas
Find
Inductor
Capacitor
Reactance
X_L = 2πfL
X_C = 1 ÷ (2πfC)
Component value
L = X_L ÷ (2πf)
C = 1 ÷ (2πf·X_C)
Frequency
f = X_L ÷ (2πL)
f = 1 ÷ (2πC·X_C)
Impedance (ideal)
Z = +jX_L
Z = −jX_C
Phase of current
Lags voltage by 90°
Leads voltage by 90°
f is in hertz, L in henries, C in farads and X in ohms. ω = 2πf is the angular frequency in rad/s.
Capacitive reactance of common values
Capacitor
50 Hz
1 kHz
100 kHz
10 MHz
10 pF
318.3 MΩ
15.92 MΩ
159.2 kΩ
1.592 kΩ
1 nF
3.183 MΩ
159.2 kΩ
1.592 kΩ
15.92 Ω
100 nF
31.83 kΩ
1.592 kΩ
15.92 Ω
0.159 Ω
10 µF
318.3 Ω
15.92 Ω
0.159 Ω
1.59 mΩ
1,000 µF
3.183 Ω
0.159 Ω
1.59 mΩ
15.9 µΩ
Inductive reactance of common values
Inductor
50 Hz
1 kHz
100 kHz
10 MHz
100 nH
31.4 µΩ
0.628 mΩ
62.8 mΩ
6.283 Ω
10 µH
3.14 mΩ
62.8 mΩ
6.283 Ω
628.3 Ω
1 mH
0.314 Ω
6.283 Ω
628.3 Ω
62.83 kΩ
100 mH
31.42 Ω
628.3 Ω
62.83 kΩ
6.283 MΩ
1 H
314.2 Ω
6.283 kΩ
628.3 kΩ
62.83 MΩ
Real components are not ideal: capacitors have series resistance (ESR) and inductance (ESL), and inductors have winding resistance and self-capacitance, so their behaviour changes near their self-resonant frequency.
Frequently asked questions
What is the formula for capacitive reactance?
X_C = 1 ÷ (2πfC), with f in hertz and C in farads, giving ohms. A 100 nF capacitor at 1 kHz has X_C = 1 ÷ (2π × 1000 × 100×10⁻⁹) ≈ 1,591.5 Ω. Doubling the frequency or the capacitance halves the reactance.
What is the formula for inductive reactance?
X_L = 2πfL, with f in hertz and L in henries. A 10 mH inductor at 50 Hz has X_L = 2π × 50 × 0.01 ≈ 3.14 Ω, and at 50 kHz it is about 3.14 kΩ. Reactance grows in proportion to frequency.
What is the difference between reactance and resistance?
Both are measured in ohms, but resistance dissipates energy as heat while reactance stores it in an electric (capacitor) or magnetic (inductor) field and returns it each cycle. Reactance also shifts the phase of the current by 90° relative to the voltage.
What is the difference between reactance and impedance?
Impedance Z combines resistance and reactance: Z = R + jX, with magnitude √(R² + X²). A pure capacitor or inductor has impedance equal to its reactance (−jX_C or +jX_L). Use the RLC impedance calculator for combined circuits.
Why does a capacitor block DC but pass AC?
At DC the frequency is 0, so X_C = 1 ÷ (2π × 0 × C) is infinite and no steady current flows. As the frequency rises, X_C falls, so high-frequency signals pass easily. An inductor does the opposite: it passes DC and blocks high frequencies.
At what frequency are X_L and X_C equal?
At the resonant frequency f₀ = 1 ÷ (2π√(LC)). There the two reactances cancel in a series circuit. This calculator shows the capacitor or inductor that would resonate with your component at the chosen frequency.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.