Helical Coil Calculator

What Is a Helical Coil Inductor?

A helical coil is a wire wound in a spiral around a cylindrical form. It stores magnetic energy and behaves as an inductor in RF circuits, filters, and antenna matching networks. Inductance depends on coil radius, length, and number of turns.

Wheeler Inductance Formula

$$L = \frac{r^2 N^2}{9r + 10l}$$

Wheeler’s approximation gives inductance $ L $ in microhenries when coil radius $ r $ and length $ l $ are in inches and $ N $ is the turn count. It works well for single-layer air-core solenoids with moderate length-to-diameter ratios.

Wire Length Estimate

Total wire length accounts for each turn’s circumference plus pitch along the coil axis. Tighter pitch increases wire usage and slightly changes the effective field distribution.

Related tools: Capacitance Converter and Cutoff Frequency Calculator.

Frequently Asked Questions

Why are radius and length converted to inches?

Wheeler’s formula is defined in inches and microhenries. The calculator converts millimeter inputs automatically before applying the equation.

Does this include a ferrite or iron core?

No. This is the air-core Wheeler approximation. A magnetic core can multiply inductance by the core permeability.

How accurate is the Wheeler formula?

It is typically within a few percent for single-layer coils where length is comparable to or greater than the diameter.

What is coil pitch?

Pitch is the axial distance advanced per turn, equal to coil length divided by turn count. It affects wire length and winding density.

Can I use this for multi-layer coils?

Wheeler’s formula targets single-layer solenoids. Multi-layer or spaced windings need more detailed models.

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What Is a Helical Coil Inductor?

Wheeler Inductance Formula

Wire Length Estimate

Frequently Asked Questions

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