There's a simple conversion that goes:
tier*(100+ee)/totier=100+ee on totier, where tier would be the actual tier of the item, and totier is the tier you're converting to.
So if you were converting say a tier 13 150 ee item to a tier 14, it would be 13*(100+150)/14=100+ee. So using a calculater the equivalent ee on a tier 14 would be ~132.
Also, there's a sort of rule people use (I don't like it but others use it), where you subtract 20 ee for each tier you go up. So in the previous example, you'd just do 150-20=130.
I prefer to be exact.
