To allow only unique values in a given range, you can use data validation with a custom formula based on the COUNTIF function. In the example shown, the data validation applied to C5:C9 is:


where emails is the named range C5:C9.

Generic formula



Data validation rules are triggered when a user adds or changes a cell value. In this example, we are using a formula that checks that the input doesn't already exist in the named range "emails":


COUNTIF returns a count of the value in C5 inside the named range emails (C5:C9). If the count is less than 2, the expression returns TRUE and validation succeeds. If not, the expression returns FALSE and validation fails.

Note: Cell references in data validation formulas are relative to the upper left cell in the range selected when the validation rule is defined, in this case B5.

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Dave Bruns

Hi - I'm Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.