This document explained how to calculate the percentile of each element and also calculating the custom percentile.
"Percentiles are very handy for exploring the distribution of number sets using various EDA graphs, including the well-known (and still underused) boxplot. The meaning of percentile can be captured by stating that the pth percentile of a distribution is a number such that approximately p percent (p%) of the values in the distribution are equal to or less than that number. So, if ‘28’ is the 80th percentile of a larger batch of numbers, 80% of those numbers are less than or equal to 28."