It is interesting that the formula for calculating the inductance of a length of microstrip on a PCB has two different expressions. A majority of calculators use the ARRL expression shown below.

L = 0.00508*b*(ln[2b/(w+h)]+0.5+0.2235(w+h/b))

where h is the separation of the strip from the ground plane and w is the width of the microstrip. b is the length of the microstrip in inches However, we found that one company substitutes 0.12963 for 0.00508 in their calculations. It is not clear why this is so and answers were not forthcoming. In the absence of justification we continue to the use the original multiplier provided by ARRL i.e. 0.00508. Please visit the Signal Processing Group Inc., website for more technical and other information.