Hello Harsh
To calculate CGPA let me take an example
Let Maths has 2 credits and Physics has 2 credits
And If you score
90-100--10
80-89--9
70-79---8
......
.....
.....
Where 10,9,8 are pointers scored in subject and Now you scored 82 Mark's in maths and 75 marks in physics
Then For maths 9 pointer and for Physics You have got 8 pointer.
Then Your CGPA would be
=(Credit*pointer)/Total credits
For this case
(2*9 +2*8)/4
Will be your CGPA .
I hope it helps.

Hello Harish

CGPA is calculated by using sgpa and number of credits 

Like in first semester your sgpa is 9 and in second semester it is 8 and number of credits in first semester is 20 and second semester is 30 than your CGPA is ( 9*20 + 8*30)/50 = 8.4 is your CGPA.

So in this way you can calculate your CGPA for all the 8 semester combine.

Good luck.