Figure 2.20: Figure 4.18 How to Choose: Flowchart for Calculating z Scores from Percentile Ranks Before calculating a z score for a percentile rank, it is a good idea to sketch out a normal distribution with both z scores and percentile ranks on the X-axis in order to estimate the answer. Once the answer is in z score format, it can be transformed to a raw score using Equation 4.3.