There is no direct conversion. 75 souls cost 25 glory, so 3 souls per glory. 700 souls cost 25 gems, so 28 souls per gem. Gems are therefore worth ~9.33x as much as glory…?
Using this indirect and very rough conversion, at 20 glory per glory chest, each glory chest “costs” about two gems.
This is a bit out of date now (I did it back in June/July and haven’t had a chance to update it since I got back) but here is a general breakdown of stuff:
