Answer

To find duplicates across sheets in Excel, use formulas, Conditional Formatting, Power Query, or PivotTables, depending on dataset size, update frequency, and visibility needs.

Method 1: Use a Formula to Identify Duplicates

What does this method do?

This method compares values in one sheet against another sheet, and flags matches directly in cells.

When should this method be used?

This method works best for small to medium datasets where real-time updates matter.

Steps

1. Select an empty column in Sheet1.

2. Enter the formula below in the first row of that column.

3. Replace A2 with the active cell reference.

4. Replace Sheet2!A:A with the column to compare against.

5. Press Enter.

6. Drag the formula down to apply it to all rows.

Formula

=COUNTIF(Sheet2!A:A, A2)>0

How does this work?

The formula counts occurrences of a value from Sheet1 inside Sheet2. A result of TRUE indicates a duplicate across sheets.

Method 2: Highlight Duplicates Using Conditional Formatting

What does this method do?

This method visually highlights duplicate values across sheets.

Steps (Windows)

1. Select the target range in Sheet1.

2. Go to Home → Conditional Formatting → New Rule.

3. Choose Use a formula to determine which cells to format.

4. Enter the formula below.

5. Click Format, choose a fill color, then click OK.

Steps (Mac)

1. Select the target range in Sheet1.

2. Go to Home → Conditional Formatting → New Rule.

3. Choose Classic as the rule type.

4. Select Use a formula to determine which cells to format.

5. Enter the same formula and apply formatting.

Formula 

=COUNTIF(Sheet2!A:A, A1)>0

What changes between Windows and Mac?

The rule selection interface differs. The formula logic stays identical.

Method 3: Find Duplicates Using Power Query

What does this method do?

This method compares entire sheets efficiently and handles large datasets.

When should this method be used?

This method works best for large tables, recurring comparisons, and automated refreshes.

Steps

1. Convert both datasets into tables using Ctrl + T.

2. Go to Data → Get Data → From Table/Range for each sheet.

3. Load both tables into Power Query.

4. Use Merge Queries.

5. Select the matching column in both tables.

6. Choose Inner Join.

7. Load the result back into Excel.

What does the result show?

The output displays only records that exist in both sheets.

Method 4: Use a PivotTable to Detect Duplicates

What does this method do?

This method aggregates data from multiple sheets and counts repeated values.

Steps

1. Combine both sheets into one table.

2. Insert a PivotTable from the combined dataset.

3. Place the comparison field into Rows.

4. Place the same field into Values.

5. Set Values to Count.

How are duplicates identified?

Values with a count greater than 1 exist in more than one sheet.

Which method should be used?

Formula-based methods suit quick checks. Conditional Formatting suits visual audits. Power Query suits large datasets. PivotTables suit summary analysis.

Key Accuracy Notes

1. Text comparisons are case-insensitive.

2. Leading and trailing spaces affect results.

3. Numbers stored as text count as different values.

4. Blank cells return FALSE unless matched with blanks.

5. Structured tables improve refresh reliability.

Common Errors and Fixes

1. Incorrect sheet names cause formula errors.

2. Merged cells break comparisons.

3. Inconsistent data types produce false negatives.

4. Hidden spaces require TRIM before comparison.

Does Excel support duplicate detection across more than two sheets?

Yes. Extend formulas by adding more COUNTIF functions joined with logical operators, or merge multiple tables using Power Query for scalable comparisons.

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