The formula for percentile is to take the number of scores below a designated number and then divide that figure by the total number of scores. A decimal results, but once it is multiplied by 100, it gives a whole number that represents the percentile rank of a score.
Percentiles are calculated to understand the strength of one number in relation to a group of numbers. For example, if a student scored 70 on a test in a class of 40 students, and 30 students scored less than 70, then the percentile would be 75. This figure is calculated by taking 30 and dividing it by 40, and then multiplying the decimal by 100 to get the percentile rank.