Indian CGPA to US GPA system
A US GPA is computed as an average of grades, mapped as follows:


A = 4
B = 3
C = 2
D = 1
F = 0


In some universities, there are interpolations between these:


A- = 3.67
B+ = 3.33


and so on for B-, C+ and so on.

I've heard of an A+ being awarded a 4.33, but that's not the case in my university where A is the maximum grade.

At least in my recollection, this maps non-linearly to the Indian CGPA system which is


A = 10
B = 8
C = 6
D = 4


Because of the non-linearity, you can't just for e.g divide your score by 2.5. Moreover, there are statistical normalizations that complicate the process. Personally, if possible, I'd just list the CGPA as is. Your transcripts will reveal the grade specifics, and that's more useful than just the summary number. I wouldn't trust the link you provided since they don't appear to provide any rationale for the mapping.

Separately I'd have a hard time seeing an Indian CGPA of 8.6 and considering it a 4.0. Even with grade inflation, that would be over optimistic.