Hey there,

Acpc merit rank is calculated from your GUJCET marks (starting from this year) earlier they used JEE main marks and its percentile. So ACPC merit marks is calculated from combining 40% of your percentile of your GUJCET marks and 60% of your percentile of PCM 12th Board Marks , whether it be GSEB, CBSE or ICSE. And according to your merit marks you will get your rank.
Example -
Suppose jee mains percentile = A
And  boards percentile = B
So your merit marks will be
(0.4A) + (0.6B) which will be out of 100.
Your ACPC merit rank will be calculated according to your merit marks.
Hope this helps!!!

Thank you.