Calculators

Inductance Calculator

Calculate inductive reactance, stored energy, resonant frequency and other useful values for inductors and coils.

What Is Inductance?

Inductance is the property of an electrical conductor or coil that opposes changes in current. It is measured in henries (H).

The symbol for inductance is L. 

Unit:

1 H = 1 henry

1 mH = 0.001 H

1 µH = 0.000001 H

An inductor stores energy in its magnetic field when current flows through it.

Inductor Symbol

──────((((((──────
          L

The voltage across an ideal inductor is related to the rate of change of current by: 

V = L × di/dt

where:

  • V = voltage in volts
  • L = inductance in henries
  • di/dt = rate of change of current in amperes per second

Inductance Calculator

Enter the inductance and frequency.

Inductive Reactance

An inductor opposes AC current through its inductive reactance.

The formula is: 

XL = 2πfL

where:

  • XL = inductive reactance in ohms
  • f = frequency in hertz
  • L = inductance in henries

As frequency increases, the inductive reactance increases.

Example — 10 mH Inductor at 1 kHz

Suppose an inductor has a value of 10 mH and operates at 1 kHz. 

L = 10 mH
  = 0.01 H

f = 1000 Hz

The inductive reactance is: 

XL = 2πfL

XL = 2π × 1000 × 0.01

XL ≈ 62.83 Ω

Therefore, the inductor has approximately 62.8 Ω of inductive reactance at 1 kHz.

Inductive Reactance Calculator

Enter inductance and frequency.

Inductor Current

The current through an inductor depends on the applied voltage and the rate at which the current changes.

Rearranging: 

V = L × di/dt

gives: 

di/dt = V / L

This means that a larger inductance causes the current to change more slowly for the same applied voltage.

Inductor Voltage Calculator

Enter inductance and current change rate.

Energy Stored in an Inductor

An inductor stores energy in its magnetic field.

The stored energy is: 

E = ½LI²

where:

  • E = energy in joules
  • L = inductance in henries
  • I = current in amperes

Inductor Energy Calculator

Enter inductance and current.

Example — 100 mH at 2 A

An inductor has an inductance of 100 mH and carries 2 A. 

L = 0.1 H

I = 2 A

The stored energy is: 

E = ½LI²

E = ½ × 0.1 × 2²

E = 0.2 J

The inductor therefore stores approximately 0.2 joules of energy.

Inductors in Series

For ideal inductors connected in series without magnetic coupling: 

LT = L1 + L2 + L3 + ...

For example: 

10 mH + 20 mH + 30 mH

LT = 60 mH

Inductors in Parallel

For ideal uncoupled inductors connected in parallel: 

1
─── = 1/L1 + 1/L2 + 1/L3 + ...
LT

For two inductors: 

L1 × L2
LT = ─────────
     L1 + L2

This is similar to the equivalent-resistance formula for resistors in parallel.

Inductors in Series Calculator

Enter at least two inductance values.

Inductors in Parallel Calculator

Enter at least two inductance values.

Inductor Current and Saturation

Real inductors have a maximum current beyond which their magnetic core may begin to saturate.

When an inductor core approaches saturation, its effective inductance can decrease significantly.

This is particularly important in:

  • Switch-mode power supplies
  • DC-DC converters
  • Output filters
  • Power amplifiers
  • Motor controllers
  • Energy-storage inductors

Inductor DC Resistance

A real inductor has winding resistance in addition to its inductance. This resistance causes power loss: 

P = I²R

The winding resistance can therefore cause the inductor to heat during operation.

Inductor Quality Factor

The quality factor, or Q factor, describes the ratio between useful reactive behavior and resistive losses.

A simplified relationship is: 

Q = XL / R

where XL is inductive reactance and R represents the relevant series resistance at the operating frequency.

A higher Q generally indicates lower relative losses.

Inductor in DC and AC Circuits

For an ideal inductor:

  • At DC steady state, it behaves approximately like a short circuit.
  • At increasing frequency, its inductive reactance increases.
  • It opposes changes in current.

Real inductors also have winding resistance, parasitic capacitance and core losses.

Inductors in Power Supplies

Inductors are widely used in switching power supplies to store energy and smooth current.

They are found in:

  • Buck converters
  • Boost converters
  • Buck-boost converters
  • Output filters
  • EMI filters
  • Power-factor correction circuits

Inductor Selection

When selecting an inductor, capacitance alone is not relevant. Important parameters include:

  • Inductance value
  • Maximum current
  • Saturation current
  • DC resistance
  • RMS current rating
  • Core material
  • Operating frequency
  • Temperature rating
  • Physical size

Common Mistakes

  • Confusing inductance with inductive reactance.
  • Using millihenries as if they were henries.
  • Ignoring the operating frequency.
  • Ignoring DC winding resistance.
  • Exceeding the inductor's saturation current.
  • Ignoring core losses at high frequency.
  • Assuming a real inductor behaves as an ideal component.
  • Ignoring parasitic capacitance in high-frequency circuits.

Key Points

  • Inductance is measured in henries.
  • Inductive reactance is XL = 2πfL.
  • Inductive reactance increases with frequency.
  • An inductor stores energy according to E = ½LI².
  • Inductors in series add their inductances when magnetically uncoupled.
  • Inductors in parallel combine according to the reciprocal formula.
  • Real inductors have resistance and losses.
  • Core saturation can reduce effective inductance.

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