We use Z Scores to transform a given standard distribution into something that is easy for us to calculate probabilities on. Why? So we can determine the likelihood of some event happening. This is a common transformation, so there is a reference chart that allows us to look up values. A simple calculator that generates a P Value from a z score. P Value from Z Score Calculator. This is very easy: just stick your Z score in the box marked Z score, select your significance level and whether you're testing a one or two-tailed hypothesis (if you're not sure, go with the defaults), then press the button! After calculating the standardized score, we need to look up the area (same as probability) using the z-table. First, we find the first two digits on the left side of the z-table. In this case it is 1.0. Then, we look up a remaining number across the table (on the top) which is 0.09 in our example.