Vol. EE Reference
Chapter 1 Useful Equations And Conversion Factors

Inductor Sizing Equation

The Inductance Formula



Wheeler’s formulas for inductance of air core coils which follow are useful for radio frequency inductors.

The following formula for the inductance of a single layer air core solenoid coil is accurate to approximately 1% for 2r/l < 3.

The thick coil formula is 1% accurate when the denominator terms are approximately equal.

Wheeler’s spiral formula is 1% accurate for c>0.2r. While this is a “round wire” formula, it may still be applicable to printed circuit spiral inductors at reduced accuracy.



The inductance in henries of a square printed circuit inductor is given by two formulas where p=q, and p≠q.



The wire table provides “turns per inch” for enamel magnet wire for use with the inductance formulas for coils.