In our institute, we are awarded a semester grade point average (SGPA) each semester; which is a weighted average of the grades in different papers, awarded out of 10.In this system:

Grade S = Grade Pt. 10
Grade A = Grade Pt. 9
Grade B = Grade Pt. 8
Grade C= Grade Pt. 7 and so on.

How can this SGPA be converted to CGPA?
Is this simply by multiplying by 0.4, i.e., SGPA 9=CGPA 3.6;
Or are there other standard means ?

Thanking anyone providing an answer,
Sam.