Heres an interesting and self-proving formula I came across recently:
MV=PT
where M=money in circulation of an economy
v=the velocity of the money circulation (how fast its exchanging hands)
p=the pricing in an economy
t=the number of transactions taking place.

this can be rearranged to find the recommended pricing:
P=MV/T
and this can also be used to show, if assuming that the V, velocity, and T, number of transactions, are constant, that inflation increases steadily with the money supply in the country.

This was proposed by John Stuart Mill who used Hume's work to base his formula. Another thing economics owes to the Great 18Th century Scottish Enlightenment.