The Central Board of Secondary Education (CBSE) prescribes a simple linear conversion:
Percentage = CGPA × 9.5
The 9.5 factor comes from CBSE's analysis of historical board results — it maps a CGPA of 10 to 95%, not 100%, because very few students score a perfect 100 in every subject. It is a guideline, not a universal law: many universities publish their own conversion tables.