Reactance Cheat Sheet

Inductive and capacitive reactance formulas with quick-lookup values at common frequencies.

Reference Reference Updated Apr 19, 2026
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Formulas

Inductive reactance
X_L = 2π · f · L (Ω)
Capacitive reactance
X_C = 1 / (2π · f · C) (Ω)
Impedance (series RLC)
Z = R + j(X_L − X_C)
|Z|
= √(R² + (X_L − X_C)²)
Phase angle
φ = arctan((X_L − X_C) / R)
Resonance
X_L = X_C at f₀ = 1 / (2π √(LC))

X_L (inductor) at common f

L 60 Hz 1 kHz 100 kHz 1 MHz
1 µH 0.38 mΩ 6.28 mΩ 0.628 Ω 6.28 Ω
10 µH 3.8 mΩ 62.8 mΩ 6.28 Ω 62.8 Ω
100 µH 37.7 mΩ 0.628 Ω 62.8 Ω 628 Ω
1 mH 0.38 Ω 6.28 Ω 628 Ω 6.28 kΩ
10 mH 3.77 Ω 62.8 Ω 6.28 kΩ 62.8 kΩ
100 mH 37.7 Ω 628 Ω 62.8 kΩ 628 kΩ
1 H 377 Ω 6.28 kΩ 628 kΩ 6.28 MΩ

X_C (capacitor) at common f

C 60 Hz 1 kHz 100 kHz 1 MHz
10 pF 265 MΩ 15.9 MΩ 159 kΩ 15.9 kΩ
100 pF 26.5 MΩ 1.59 MΩ 15.9 kΩ 1.59 kΩ
1 nF 2.65 MΩ 159 kΩ 1.59 kΩ 159 Ω
10 nF 265 kΩ 15.9 kΩ 159 Ω 15.9 Ω
100 nF 26.5 kΩ 1.59 kΩ 15.9 Ω 1.59 Ω
1 µF 2.65 kΩ 159 Ω 1.59 Ω 0.159 Ω
10 µF 265 Ω 15.9 Ω 0.159 Ω 16 mΩ
100 µF 26.5 Ω 1.59 Ω 16 mΩ 1.6 mΩ

Notes

  • Reactance is the imaginary part of impedance — pure inductors and capacitors store energy; ideal ones dissipate none.
  • At resonance, reactive parts cancel and the circuit presents pure R.

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