It is very simple to convert your obtained percentage into CGPA.

Percentage to CGPA*

For 4-point credit system, You have to do (Percentage - 20) / 18 = Equivalent CGPA*
Eg: If Percentage is 74%, then the equivalent CGPA = (74 - 20) / 18= 3.00*

For 10-point credit system, You have to do (Percentage) / 9.3 = Equivalent CGPA
Eg: If Percentage is 83.7%, then the equivalent CGPA = 83.7 / 9.3 = 9.00