Comprehensive Guide to Air Coil Inductors in Millimeters
Air core inductors are essential elements in high-frequency radio applications, oscillators, and RF filter designs. Because they lack a ferromagnetic core, they do not suffer from core saturation or nonlinear magnetic losses, making them highly predictable and reliable at high frequencies.
Formula Used
This calculator relies on Wheeler's classic approximation formula adapted for single-layer air solenoids. The mathematical formulation calculates inductance $L$ in microhenries based on diameter $D$ and length $L$ measured in millimeters:
$$L (\mu H) = \frac{0.03937 \cdot D^2 \cdot N^2}{18 \cdot (0.03937 \cdot D) + 40 \cdot (0.03937 \cdot l)}$$
Where $D$ is the coil diameter, $l$ is the winding length, and $N$ represents the total number of turns.
How to Use This Calculator
- Enter your custom coil diameter ($D$) in millimeters inside the first column.
- Specify the total axial winding length ($l$) and number of turns ($N$).
- Input your wire diameter and pick the appropriate conductor material.
- Provide your target operating frequency to compute reactance.
- Press the calculate button to review comprehensive outputs instantly above the form.
Frequently Asked Questions (FAQs)
Millimeter sizing provides high accuracy for custom small-scale RF components, PCB traces, and hand-wound toroidal or cylindrical inductors.
A warning will trigger indicating that windings overlap, meaning turns are physically packed too tightly for the chosen wire gauge and length.