Many Anna University students need a percentage for a job form, a higher-study application, or a scholarship, even though their result sheet shows a CGPA. The first step is to start with your final CGPA, not a single-semester SGPA, because a semester result is only one part of the whole degree.
For Anna University, the conversion is simple:
Percentage = CGPA x 10
You multiply the CGPA by ten, and the result is the percentage.
For example, a CGPA of 8.0 gives 8.0 x 10 = 80%. A CGPA of 8.5 gives 8.5 x 10 = 85%. Another check is 7.6 x 10 = 76%, which shows the same method works for any CGPA value.
To do it yourself, read the final CGPA from your mark sheet, multiply it by ten, and write the CGPA beside the percentage on the form. That way, anyone checking the form can see how the percentage was worked out, and you avoid confusion later.
Do not borrow another method for this result. The CBSE method of multiplying by 9.5, and methods that subtract 0.75 before multiplying, belong to other systems. Using them for an Anna University CGPA would give a different percentage, even though the starting CGPA is the same.
For rounding, keep the decimal if your form allows it. A CGPA of 8.25 gives 8.25 x 10 = 82.5%, not a rounded-up 83%, unless a form specifically asks for a whole number. A dedicated Anna University guide is coming, with more worked examples for this conversion.
You can check your result with a CGPA to percentage calculator.
Before you submit any form, double-check the CGPA digits against your mark sheet, keep the calculation with the application, and use the same percentage on every copy of that form so the figures match. If the digits do not match, correct the form before you send it.