The Z score is calculated in Google Sheets using the = (DataValue - Mean) / Standard Deviation formula. Therefore, you have to find the Mean and Standard Deviation first. To find the Mean, use the =AVERAGE(value set) formula and enter all of your values by highlighting them. The Standard Deviation can be found by typing in the =STDEV(value set) formula. Another way to quickly find the Z score is to check the Z score table or memorize them, as they always remain the same. The Z score for a 90% Confidence Interval is 1.645, for 95% - 1.96, and for 99% - 2.576.