How do you convert from using 64 pitch to 48 pitch? Seems like I may have more flexibility with gearing in 48 pitch since I have tons of spurs and pinions collected over the years. But how do you convert from one pitch to another and have a reasonable overall gear ratio?

Of course, the non-scientific way would be to take an existing 64 pitch spur and pinion combination and try to physically match it up a 48 pitch spur and pinion combination so that they are all the same physical size.

Barring that trial and error, is there a scientific / mathematical way to convert from 64 pitch to 48 pitch?

Thanks in advance.