Method 1: UNIQUE + COUNTA (Modern)
Excel 365 / Google Sheets: =COUNTA(UNIQUE(A2:A100))
Method 2: SUMPRODUCT (Legacy)
Works in all Excel versions: =SUMPRODUCT(1/COUNTIF(A2:A100,A2:A100))
Method 3: COUNTIFS for Conditional Unique
Count unique values where another column meets a condition.
Platform Notes
UNIQUE() is available in Excel 365 and Google Sheets. For older Excel versions, SUMPRODUCT is the only option. Google Sheets also supports =ROWS(UNIQUE(A2:A100)) as an alternative.