Most probably, you are concerned because of the percentage field that appears when applying for PSUs (via GATE), IIMS (via CAT), or foreign universities.
Unfortunately, IIEST Shibpur follows no CGPA to percentage conversion rule.
The authorities will tell you to use the absolute percentage, which is less than CGPA*10. They will simply provide you in writing that IIEST doesn’t have a CGPA to percentage conversion rule.
It is difficult to score good grades in most departments, and added to it is the lack of a proper conversion system. This causes major disadvantage for IIM aspirants, job aspirants, and those applying to foreign universities.