Sorry, but this is a common mistake. It was actually derived from the slightly deranged English way of working out what size penny farthing front wheel the gear is equivalent to.

If you place a mark on the ground, place a crank vertically above it and wheel the bike backwards in a straight line, until the crank has made one full revolution, that will tell you how far the bike will travel forward for each crank revolution. You will find that it is much more than the gear inches given by the traditional formula.

Europeans have always used the above system for measuring the gear and it is much more sensible.