Inductor Calculator
Calculate inductance, inductive reactance, stored magnetic energy, or RL time constant from common circuit values.
What Is an Inductor?
An inductor is a passive electronic component that stores energy in a magnetic field when current flows through it. Its key property is inductance (L), measured in henries (H). In practical circuits, inductors are used in power supplies, filters, RF matching networks, motor control systems, and many other analog and digital designs.
If you have ever worked with a buck converter, crossover network, or EMI filter, you have already seen inductors in action. This calculator helps you quickly solve common design equations so you can move from idea to prototype faster.
Core Inductor Formulas
1) Inductive Reactance
The effective AC opposition of an inductor is called inductive reactance:
XL = 2πfL
- XL = reactance in ohms (Ω)
- f = frequency in hertz (Hz)
- L = inductance in henries (H)
2) Energy Stored in an Inductor
Inductors store magnetic energy based on current:
E = ½LI²
- E = energy in joules (J)
- L = inductance in henries (H)
- I = current in amperes (A)
3) RL Time Constant
In an RL circuit, current rise and decay are described by the time constant:
τ = L / R
- τ = time constant in seconds (s)
- L = inductance in henries (H)
- R = resistance in ohms (Ω)
How to Use This Inductor Calculator
Step-by-step workflow
- Select the calculation type from the dropdown.
- Enter your known values and choose units carefully.
- Click Calculate to see the result and formula reference.
- Use Clear to reset values and start a new case.
The calculator automatically converts unit prefixes (mH, µH, nH; kHz, MHz, GHz), reducing conversion mistakes.
Practical Design Notes
Frequency matters a lot
Inductive reactance grows linearly with frequency. An inductor that looks almost like a short at low frequency can look highly resistive at high frequency. Always calculate XL at your exact operating frequency.
Real inductors are not ideal
Physical inductors include winding resistance (DCR), core losses, and parasitic capacitance. At high frequency, these parasitics can dominate behavior and shift results away from simple equations. Treat this calculator as a first-pass engineering tool, then verify with component datasheets and measurements.
Saturation current is critical in power circuits
In DC-DC converters and motor drivers, choose an inductor with sufficient saturation current. If core saturation is reached, effective inductance can drop sharply, increasing ripple current and thermal stress.
Example Use Cases
AC filter design
Suppose you want 100 Ω of inductive reactance at 1 kHz. Using L = XL / (2πf), the required inductance is about 15.9 mH. That quickly narrows your component search.
Estimating magnetic energy
A 10 mH inductor carrying 2 A stores E = ½LI² = 0.02 J (20 mJ). This helps evaluate pulse handling and transient behavior.
Timing behavior in RL switching
For L = 100 mH and R = 200 Ω, τ = 0.5 ms. After one time constant, current reaches about 63% of final value. After roughly 5τ, the transition is essentially complete.
Common Mistakes to Avoid
- Mixing Hz and kHz (or MHz) without converting.
- Entering µH values as H by accident.
- Using DC formulas to predict full high-frequency behavior of real inductors.
- Ignoring resistance and core limits in power applications.
Final Thoughts
A good inductor calculator saves time, improves design intuition, and helps catch unit errors before they become expensive. Use this tool for quick calculations, then validate with simulation and bench testing for production designs.