You will also find a formula to count unique values, see the table of Contents below. Unique values are values that exist only once in a list or cell range. If a value has a duplicate they are not unique and not counted.
If you are working with lots of data I highly recommend using a pivot table. Excel 2013 and later versions allow you to count unique distinct values.
Question: How do I count unique distinct values in two ranges combined? Answer: Formula in D14: =SUM(1/(COUNTIF(Table1, Table1)+COUNTIF(Table2, Table1)))+SUM(1/(COUNTIF(Table2, Table2)+COUNTIF(Table1, […]