To find the average for a measure in tableau, right click on the measure and select average:
Definition: The average is also known as the mean in statistics. This is the sum of values divided by the number of observations.
The formula for the mean or average is:
Tip: Averages are very commonly used to summarize large amounts of data, but often they don't give you an accurate or whole data story. For instance, averages are influenced by outliers (large or small data points relative to your data). In these cases, the median may be a better statistic as this indicates the middle data point.