1. Open your Google Sheet and select the range
Launch Google Sheets and highlight the cells where you want to check for duplicates (e.g., a single column or a full table).
2. Open the Conditional Formatting panel
Click Format in the top menu, then choose Conditional formatting to open the sidebar on the right.
3. Choose “Custom formula is”
Under the Format cells if dropdown, scroll to the bottom and select Custom formula is.
4. Use the COUNTIF formula
Use the COUNTIF formula. For example, to check Column B for duplicates, we'll use =COUNTIF(B$2:B$41, B2) > 1. This flags any value that appears more than once within the selected range.
5. Set a highlight color
Choose a fill color under Formatting style to visually mark duplicates, then click Done.
6. Review highlighted duplicates
All duplicate values in your selected range should now be highlighted automatically.
