if you and nine other people took a test and your score is ninety one out of a hundred it doesn't necessarily mean you did well what if it was an easy test and everyone else got a higher score percentiles also called San tiles are here to help paint a more specific picture if only one person got a higher score and eight people did worse than you we say you're at the 80th percentile or that the percentile rank is 80 because 80% of the test scores are below yours we calculate this rank by simply dividing the number of values below 91 in our case 8 by the total number of values in our case 10 and then multiplying that by 100 being at the 80th percentile should not be confused with being in the 80th percentile which means your value is either lower or equal to the value that's at the 80th percentile let's assume the ten grades are as follows ordered from lowest to the highest 4450 58 60 to 70 388 e5 90 91 98 your score 91 is the only one which is at the 80th percentile or has a percentile rank of 80 all of the lower scores and also yours are in the 80th percentile whereas 98 is the only one which isn't in the idea percentile simple enough if magically two score of the person right below you gets increased to 91 which is also your score things get tricky some would say you're at the 70th percentile now because only seven scores are lower than yours whereas other state you're still at the 80th percentile because they believe that score equal to yours should also be counted so yeah there's no clear consensus on this and while for large data sets it doesn't make that much of a difference it counts for smaller data sets like ours so to be transparent always state which approach you're using if we split the data into ten percent groups we can also say first decile instead of ten percentile if we split it into 25% groups who can say first quartile instead of 25th percentile and so on our final note please don't confuse percentile with percentage or in our case the 80th percentile which tells you how you score compared to others with the ninety-one percent percentage which tells you which percentage of the maximum possible score you obtained