Inductance Calculator

About the Inductance Calculator

The Inductance Calculator computes the inductance of common inductor geometries: single-layer solenoids, multilayer coils, and toroidal cores. Inductance (measured in Henrys) describes a coil's ability to store energy in a magnetic field and resist changes in current — it is fundamental to filters, power supplies, RF circuits, transformers, and energy conversion.

For a solenoid, inductance depends on the number of turns squared, core area, core length, and permeability of the core material. Adding a ferrite or iron core dramatically increases inductance compared to an air-core coil. This calculator also provides inductive reactance (X_L = 2πfL), Q-factor estimate, RL time constant, and stored energy at a given current.

Enter the coil parameters to calculate inductance, impedance, and energy storage. Compare different geometries and core materials, and see how changing turns or dimensions affects the result. It gives you a quick sanity check before you wind or spec a coil. That saves time when you are testing a design on paper first.

When This Page Helps

Use this calculator when you need a quick inductance estimate before winding or prototyping a coil. It is useful for filter design, power-supply chokes, RF coils, and sanity-checking how geometry or core material changes the result. That makes it easier to compare a layout against the target inductance upfront. It is especially handy when the coil dimensions are still being adjusted.

How to Use the Inputs

1. Select the inductor geometry: solenoid, toroid, or multilayer coil.
2. Enter the number of turns.
3. Enter the coil dimensions (diameter, length, core area).
4. Select the core material (air, ferrite, iron powder, etc.).
5. Enter the operating frequency for reactance and impedance calculations.
6. Enter DC resistance and current for Q-factor and energy calculations.
7. Review inductance, reactance, impedance, time constant, and energy.

Example Calculation

Tips & Best Practices

• Winding turns close-packed and evenly spaced gives the most predictable inductance.
• For RF coils, air-core or low-μ powdered iron is preferred — low loss and no saturation.
• Ferrite cores are frequency-selective: NiZn ferrite for >1 MHz, MnZn ferrite for <1 MHz.
• Toroidal shapes contain the magnetic field — less EMI than solenoids, ideal for sensitive circuits.
• At high frequency, parasitic capacitance between turns creates a self-resonance that limits usable bandwidth.
• Litz wire reduces skin effect losses in RF inductors — use it above 50 kHz.

Solenoid vs Toroid vs Multilayer Coil

Single-layer solenoids are easy to wind and calculate but radiate magnetic field, causing EMI. Toroids confine the field within the core, minimizing radiation — ideal for power supplies and sensitive analog circuits. Multilayer coils achieve high inductance in small volume but have higher parasitic capacitance and are harder to model accurately. Each geometry has its niche in electronics design.

Core Material Selection

Air core: zero core loss, no saturation, lowest inductance per turn. Used in RF tuned circuits, Tesla coils, and high-frequency filters. Iron powder: moderate μ (3-75), gradual saturation (soft), low cost. Used in EMI filters and power line chokes. Ferrite: high μ (100-15,000), sharp saturation, frequency-dependent losses. Used in switching power supplies, transformers, and RF chokes. Amorphous/nanocrystalline: very high μ (10,000-100,000), low loss. Used in high-efficiency power inductors and current sensors.

Inductor Design for Switching Power Supplies

In buck/boost converters, the inductor stores and releases energy each switching cycle. Key parameters: inductance (L = V × D × T_s / ΔI), saturation current (I_sat > I_peak), DC resistance (low for efficiency), core loss (depends on frequency and flux swing). Typical design targets ripple current at 20-40% of DC current. Core selection starts with energy storage: E = ½LI² must fit within the core's LI² rating.

Frequently Asked Questions

• What is inductance?

  Inductance (L, in Henrys) measures a coil's opposition to changes in current. When current changes, the coil generates a voltage (back-EMF) proportional to the rate of change: V = L × dI/dt. A 1 Henry inductor produces 1 volt when current changes at 1 amp per second. Practical inductors range from nanohenrys (nH) to henrys.

• How does core material affect inductance?

  Core permeability (μᵣ) multiplies the air-core inductance. Air: μᵣ=1. Iron powder: 3-100. Ferrite: 100-15,000. Laminated iron: 300-10,000. Higher permeability = higher inductance for the same coil. But high-μ cores saturate at lower flux density and have higher core losses at high frequency.

• What is the Q-factor of an inductor?

  Q = X_L / R = 2πfL / R_dc (approximately). Higher Q means less energy loss per cycle. Good air-core RF inductors: Q = 100-300. Ferrite-core: 50-200. Iron-core power inductors: 10-50. Q is maximized at a specific frequency — above it, parasitic capacitance and skin effect reduce Q.

• Why does a solenoid's inductance depend on N²?

  Each turn contributes flux, and each turn also links to the flux from all other turns. With N turns, the total flux linkage is N times the flux per turn, which itself is proportional to N (from N turns of current). So total inductance ∝ N × N = N². This is why doubling turns quadruples inductance.

• What is the Nagaoka correction factor?

  The simple solenoid formula (L = μN²A/ℓ) assumes an infinitely long coil. Real coils have end effects that reduce inductance. The Nagaoka factor K_N (0 < K_N ≤ 1) corrects for the coil's length-to-diameter ratio. Short, wide coils have K_N much less than 1; long thin coils approach K_N = 1.

• How do I measure inductance?

  Use an LCR meter (most accurate), or measure the resonant frequency with a known capacitor (f_res = 1/2π√(LC), then L = 1/(4π²f²C)). For rough estimates, measure the RL time constant with an oscilloscope and known resistor. Most DMMs cannot measure inductance accurately.