What formula is used for inductance?

The ideal solenoid formula: L = μ₀ × N² × A / l. μ₀ = 4π × 10⁻⁷ H/m is the permeability of free space. This assumes air-core with a length much greater than the radius.

Can I use a diameter instead of area?

Yes. Toggle the input mode to "Diameter" and the tool computes the cross-sectional area as A = π × (d/2)².

What is inductive reactance?

Inductive reactance XL = 2πfL is the opposition a coil presents to alternating current at frequency f. Higher frequency or higher inductance means higher reactance (in ohms).

Does this account for core material?

No. The formula assumes an air core (relative permeability μᵣ = 1). For ferromagnetic cores multiply L by μᵣ of the core material.

What are typical units for inductance?

Henry (H) is the SI base unit. Practical coils are usually in millihenries (mH, 10⁻³ H) or microhenries (μH, 10⁻⁶ H).

How do I increase a coil's inductance?

Inductance rises with the square of the turns (L ∝ N²), so doubling the turns gives roughly four times the inductance. You can also increase the cross-sectional area, shorten the coil length, or add a ferromagnetic core (which multiplies L by the core's relative permeability μᵣ).

Inductance Calculator

Calculate the inductance of a solenoid coil and its inductive reactance at a given frequency.

Coil Parameters

Number of Turns (N)

Coil Length

Cross-sectional Area

Frequency (optional — for X_L)

Fill in the coil parameters and press Calculate.

Summary

This tool calculates the self-inductance of a solenoid coil using the formula L = μ₀ × N² × A / l, where μ₀ is the permeability of free space (4π × 10⁻⁷ H/m), N is the number of turns, A is the cross-sectional area in m², and l is the coil length in meters. It also computes inductive reactance XL = 2πfL at a specified frequency.

How it works

Enter the number of turns (N) and the coil length.
Enter the cross-sectional area, or switch to diameter mode to enter the coil diameter.
Optionally enter a frequency to also compute inductive reactance.
The tool applies L = μ₀ × N² × A / l and returns inductance in henries, auto-scaled to mH or μH.
Inductive reactance XL = 2πfL is shown in ohms when a frequency is provided.

Use cases

Design RF coils and chokes for electronics projects.
Determine inductance for power-supply filter inductors.
Verify coil parameters before winding a transformer.
Calculate inductive reactance for AC circuit analysis.
Teach or learn electromagnetic theory with live calculations.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu