Calculator Inputs
Example Data Table
| Method | Example Inputs | Expected Inductance | Use Case |
|---|---|---|---|
| Voltage ramp | 12 V, ΔI = 2 A, Δt = 5 ms | 30 mH | Switching coil test |
| Energy | E = 0.5 J, I = 2 A | 250 mH | Stored energy check |
| Reactance | XL = 62.83 Ω, f = 1000 Hz | 10 mH | AC impedance measurement |
| Resonance | f = 1591.55 Hz, C = 1 µF | About 10 mH | LC tank circuit |
| Solenoid | N = 500, d = 30 mm, l = 100 mm, μr = 1 | About 2.22 mH | Air core coil design |
Formula Used
Voltage ramp: L = V × Δt / ΔI. This uses induced voltage and current change over time.
Stored energy: L = 2E / I². This uses magnetic energy stored in the inductor.
Reactance: L = XL / 2πf. This uses inductive reactance at a known frequency.
Resonance: L = 1 / ((2πf)² × C). This uses resonant frequency and capacitance.
Solenoid: L = μ0 × μr × N² × A / l. This estimates a straight coil.
Toroid: L = μ0 × μr × N² × A / 2πr. This estimates a toroidal core.
Series network: Leq = L1 + L2 + L3. Inductances add directly in series.
Parallel network: 1 / Leq = 1 / L1 + 1 / L2 + 1 / L3. Reciprocals add in parallel.
Coupled inductors: Leq = L1 + L2 ± 2M, where M = k√(L1L2).
How to Use This Calculator
- Select the calculation method that matches your known data.
- Enter values in the shown fields. Use positive values only.
- Add analysis frequency, resistance, current, and tolerance if needed.
- Press the calculate button to show results above the form.
- Review henry, millihenry, microhenry, tolerance, reactance, and energy outputs.
- Use the CSV or PDF button to save the calculation report.
Why Circuit Inductance Matters
Inductance describes how strongly a circuit resists current change. It is central to filters, motors, relays, power supplies, antennas, and sensing coils. A correct value helps engineers predict ripple, switching stress, resonance, noise, and stored magnetic energy. Small errors can shift cutoff points or create overheating.
Advanced Calculation Options
This calculator supports several practical methods. Use the voltage method when a measured voltage and current ramp are available. Use the energy method when stored magnetic energy is known. Use reactance when impedance is measured at a known frequency. Use resonance when capacitance and resonant frequency are known. Geometry modes estimate air core solenoid and toroid values from turns, dimensions, and permeability. Network modes combine many inductors in series, parallel, or coupled arrangements.
Design Notes
Real inductors are not perfect parts. Copper resistance, core loss, saturation, frequency, winding capacitance, and layout affect measured behavior. A ferrite or iron core can raise inductance, yet it can saturate under high current. Air core coils avoid saturation, but they often need more turns. Long wires and board traces also add small inductance. High speed circuits should consider this parasitic value.
Interpreting Results
The main result is shown in henries, millihenries, and microhenries. Extra outputs show tolerance limits, reactance at a selected frequency, RL time constant, cutoff frequency, and stored energy. These values help compare parts and validate a circuit quickly. For production work, confirm results with measurements and vendor data.
Good Measurement Practice
Measure inductance under conditions close to the final circuit. Keep lead length short. Use the correct test frequency. Avoid core saturation during tests. Record tolerance, current rating, and temperature. When using resonance, choose a stable capacitor with low loss. When using current ramp data, measure the actual time interval and current change carefully.
Common Applications
Power converters use inductors to smooth current and store energy. Audio crossovers use inductance to shape speaker response. RF circuits use coils for tuning and impedance matching. Relays and solenoids depend on magnetic fields. The same formulas help across these areas, but real layouts still require testing. For safer choices, add margin above peak current. Check heating during long operation. Recalculate after changing frequency, wire size, turns, or core material in prototypes.
FAQs
What is inductance?
Inductance is the ability of a circuit or coil to oppose current change by storing energy in a magnetic field.
Which method should I choose?
Choose the method that matches your known values. Use reactance for AC tests, resonance for LC tanks, and geometry for coil design.
What unit does the calculator return?
The calculator returns henries first. It also converts the same result into millihenries and microhenries for easier comparison.
Can I calculate parallel inductors?
Yes. Select the network method, choose parallel, enter values separated by commas or spaces, then submit the form.
Does core material affect inductance?
Yes. Higher relative permeability usually increases inductance. Core saturation, losses, and frequency still affect real circuit behavior.
What is coupling coefficient?
Coupling coefficient describes magnetic linking between two inductors. It ranges from zero for no coupling to one for ideal coupling.
Why is measured inductance different?
Lead length, test frequency, winding resistance, core loss, saturation, and stray capacitance can change measured inductance.
Can this replace lab testing?
No. It helps with design estimates and checks. Critical circuits should be verified with measurements and component data sheets.