No, it is never advisable to attempt a conversion. There can be no conversion cchart and it would make absolutely no sense. So even if someone said a BA degree from India can be convertd into GPA via XYZ routes, and someone had a 65% in English literature from india (which may be exceptionally good in many Indian universities, for literature is sooooo stringently graded), then that person would get a very low GPA.
Universities know this very well as you arent the first one with this problem. I'vce applied to many US unis for PhDs and got through and nowehere did I even attenpt to convert my marks.