Arrange the scores in order from lowest to highest. For example, if your assessment scores are 8, 3, 6, 32, 32, 33, 37, 37, 9, 17, 19, rearrange them to appear in the order 3, 6, 8, 9, 17, 19, 32, 32, 33, 37, 37.
Find the score whose percentile rank you wish to assess. For example, you may choose to assess the percentile rank of the score 32. Note that in this example, there are two scores of 32.
Multiply the number of scores that are equal to the score you are interested in by 0.5. In this example, you would multiply 2 by 0.5 since there are two scores of 32. This will give you a result of 1.
Add this figure to the number of scores that rank below the score you are interested in. In our example, there are six scores that rank below 32. Add 6 + 1 for a result of 7.
Divide this result by the total number of assessment scores in the group. In this example, there are eleven scores. Therefore, you would divide 7 by 11 and obtain a result of 0.636.
Multiply this result by 100. 0.636 multiplied by 100 is equal to 63.6. Therefore, in our example the score of 32 is equal to the 63.6 percentile rank *or 64th percentile rank if you prefer to round up).