Here is my collection of useful calculators and other tools. Mostly borrowed from other sites as I found them so useful that if those websites ever went dark I’d have to lose time figuring out how to recreate it again from scratch.

Inductance Calculator - Impedance Comparison to Resistor

This Inductance calculator was created by Tim Daycounter at www.daycounter.com

Place the inductor in series with a known resistor of good precision, for example a 100 ohm 1% resistor is a good choice. Stimulate the circuit with a function generator, and view the junction between the resistor and inductor on the scope, as well as the input voltage. Tune the function generator until the junction voltage is half the input voltage. The relationship between R and L is, as derived below:

L= R*sqrt(3)/(2*pi*f)

The advantage of this method is that it is accurate in that calibration resistors can be found with tolerances in the 0.1% range.

It should also be noted that this applies for capacitors but the formula is slightly different with R on the bottom:

C= sqrt(3)/(2*pi*F*R)

Derivation of relationship between R and L when |Vo|= ¹⁄₂|Vs|

First use the formula for a voltage divider: Vo/Vs= Z1/(Z1+Z2)

Vo/Vs= *R/(R+j*w*L)

Next compute magnatude squared by multiplying each by complex conjugate:

| Vo |^2 / |Vs|^2 = | *R/(R+j*w*L) |^2

We care about the Vo/Vs = ¹⁄₂:

|¹⁄₂|^2 = R^2 / ( R^2+ (w*L)^2 )

4*R^2= R^2+ (w*L)^2

R= w*L/sqrt(3)

L= R*sqrt(3)/(2*pi*f)