How to Change a T-Score to a Percentile Rank

T-scores represent a standardized score that corresponds to standard deviations. Standard deviations measure the variance of a particular value from the mean, or average result of the population. Percentiles express the relative ranking of a given value out of the total population. Each standard deviation from the mean encompasses a set percentage of a normally distributed population. Knowing your T-score allows you to calculate your percentile rank.

Instructions

• 1

  Convert a T-score to a standard deviation. Check with the methodology disclosure for the score. Typically the mean has a T-score of 50 and each standard deviation is 10 points. For example, if the T-score is 65 then it is +1.5 standard deviations.

• 2

  Add up percentages of population contained within each standard deviation. All values up to 0 standard deviation contains 50 percent of the population. Refer to a chart showing the percent of a population within each standard deviation. For example, +1.5 standard deviations contain 42.3 percent of the population.

• 3

  Round the value down to the nearest integer. Percentiles express how far the value is from the bottom of the data set and are always whole numbers. Express that value as the percentile rank. For example, +1.5 standard deviation is higher than 50 percent (0 standard deviation) plus 42.3 percent (+1.5 standard deviation). However, it represents the 92nd percentile.