Coil Inductance

Results

Calculate the inductance of a single-layer air core coil using Wheeler’s approximation formula. Used in RF circuits, antenna design, Tesla coils, radio tuning circuits, and custom inductor winding projects.

Wheeler’s Formula: L (µH) = (N² × D²) ÷ (18D + 40l)N = turns, D = coil diameter (inches), l = coil length (inches)

Results

How to use this calculator

Step-by-Step Instructions

1. **Count the turns** Count the total number of wire loops in your coil.
2. **Measure the diameter** Measure the outer diameter of the coil in inches (1 inch = 25.4mm).
3. **Measure the length** Measure the length of the wound portion of the coil in inches.
4. **Click Calculate** The inductance is displayed in µH and mH.

Pro Tips

Wheeler’s formula is most accurate when the coil length is greater than 0.4× the diameter.

To convert mm to inches, divide by 25.4 (e.g., 25mm = 0.984 inches).

This formula applies to single-layer air core coils only. Multi-layer or ferrite core coils require different formulas.