Inductance calculator

Electricity
75 calculations
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📝 How it works:
Calculates the magnetic energy and reactance of a coil for a given inductance, current and frequency

Fill in the fields below and click "Calculate".

Inductance calculator: Magnetic energy and reactance

Coils (inductors) store magnetic energy and exhibit frequency-dependent reactance. Our calculator calculates:

  • Magnetic energy: E = ½ × L × I² (stored in the magnetic field)
  • Reactive resistance: X_L = 2π × f × L (increases with frequency)
  • Filter design: LC filter, crossover for loudspeakers
  • Transformers: Inductance primary/secondary
  • Switching power supplies: dimensioning storage chokes

Important correlations:

  • E = ½LI²: Energy in the magnetic field (analogous to E = ½CU² for a capacitor)
  • X_L = ωL = 2πfL: Inductive reactance increases with frequency
  • U = L × dI/dt: Self-induction voltage with current change

Units:

  • H (Henry) = Vs/A - Very large, rarely used
  • mH (Millihenry) = 10-³ H - line filter, audio
  • µH (microhenry) = 10-⁶ H - HF coils, SMPS
  • nH (nanohenry) = 10-⁹ H - conductor paths at high frequencies

Example: A 100µH coil at 10A stores E = 0.005 joules. At 50Hz: X_L = 31.4 mΩ (almost short circuit). At 100kHz: X_L = 62.8 Ω (considerable resistance). Coils therefore act as a low-pass filter: low frequencies through, high frequencies blocked. Opposite of the capacitor!

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