Coil Inductance
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.
Air-core single-layer coil
Inductance (Wheeler)2.041 H
FormulaL(µH) = (N² × D²) ÷ (18D + 40l)
Accuracy±1–5% for practical coils
Formulas used
Wheeler’s Formula: L (µH) = (N² × D²) ÷ (18D + 40l)N = turns, D = coil diameter (inches), l = coil length (inches)
How to use this calculator
Step-by-Step Instructions
- Count the turns Count the total number of wire loops in your coil.
- Measure the diameter Measure the outer diameter of the coil in inches (1 inch = 25.4mm).
- Measure the length Measure the length of the wound portion of the coil in inches.
- 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.