Percentile is a relative term and tells where you stand in a set of people. For example, if you have 99.95 percentile in GATE 2012 means that your score or marks are above 99.95% student who took GATE 2012 exam.Whereas, percent is a relative and measured on the scale of 100, it means that how many marks you got out of 100. This is not a measure of GATE performance. Therefore, don’t worry if someone says you that they go 99.9X score and think that it is beyond your capacity. To answer how to find GATE 2012 percentile please read the below formula and example carefully.
The GATE 2012 percentile is calculated as follows:
P = ( (N- your rank)/ N) x 100

Where P is percentile and N is total number of candidates appeared for GATE 2012 exam in your stream.
(N- Your rank) indicates the number of candidates who have scored more marks than you.
For example, if total number of candidates are 100 and 90 of them have less marks than you P = (09/100)X100 = 0.9×100 = 90 percentile.
For another example: A guy form Mechanical Engineering have All India Rank (AIR) 99 and total number of student of candidates appeared for the GATE 2012 Electronics and Communication Engineering are 1,76,944 in GATE 2012. Then his GATE 2012 percentile would be calculated as
P = ((176944-99)/ 176944) X 100 = 99.944
The candidate has 99.94 percentile.