Apparently it is not what the OP was looking for but since it became part of the discussion...I used Gear Inches a lot to help me make decisions about my own drivetrain and everybody seems to be forgetting that tire size, which does effect the actual wheel diameter, should be included to more precisely calculate G/I. I'm pretty sure I've seen a formula somewhere that factors it in, but that's one of the reasons, besides being kinda lazy, why I am content to use one of the abundant gearing calculators available on the interwebz.

And to be precise, seeing as how it was just mentioned that crankarm length ought to be included in one's gear calculations - No, that is not any part of figuring Gear Inches (or the European/Metric equivalent - "Meters of Development"). It is Sheldon Brown's gear measurement system called "Gain Ratio," which is the distance travelled by the bike divided by the distance travelled by the pedals during one turn of the crank, that does bring crankarm length into the equation....