How to Compare Two Excel or CSV Files and Find the Differences

Someone sends you an updated price list, the new export of your customer list arrives, or two colleagues edited copies of the same sheet. Scrolling through both looking for differences takes ages and misses things. Comparing the two files does it in seconds and shows exactly which rows were added, removed or changed.

This guide shows how to compare two spreadsheets with the free File Comparison tool, and how to prepare them so the result is clear.

Step 1: save both sheets as CSV

File Comparison compares text, and a CSV file is a spreadsheet as text: one row per line, cells separated by commas. Excel files (.xlsx) are packed binary files and can’t be compared directly, so export both versions first:

• Excel: File › Save As › CSV UTF-8 (Comma delimited).
• Google Sheets: File › Download › Comma-separated values (.csv).
• LibreOffice and Numbers: Save As or Export as CSV.

Export both the same way, so numbers, dates and separators are written identically.

Step 2: sort both the same way (this matters most)

The comparison works line by line, in order. If the rows are in a different order in the two files, unchanged rows look like they were removed in one place and added in another. Here is an old and a new version of a small price list:

sku,product,price,stock
A100,Blue mug,12.90,40
A101,Red mug,12.90,25
A102,Teapot,34.00,8
A103,Coaster set,9.50,60

sku,product,price,stock
A100,Blue mug,12.90,40
A101,Red mug,13.50,25
A103,Coaster set,9.50,60
A104,Tea towel,7.90,30

Sorted the same way, by sku, File Comparison finds exactly what happened: 1 modified row (the red mug’s price went from 12.90 to 13.50), 1 removed (the teapot) and 1 added (the tea towel). With the same data shuffled into a different order, it reports 3 rows removed and 3 added instead, which is much harder to read.

So before exporting, sort both sheets by the same column, ideally one that never changes, such as an ID, SKU, email address or order number (in Excel: Data › Sort). Also keep the same columns in the same order in both files.

Step 3: compare

1. Open File Comparison. Click Upload File on the left (Left / Original) for the old version and on the right (Right / Target) for the new one, or paste the text.
2. If needed, tick Ignore whitespace or Ignore case, so that extra spaces or a different capitalisation don’t count as changes.
3. Click Compare. The summary tells you how many change blocks there are, such as 2 change blocks: 1 added, 1 removed, 1 modified lines.

Reading the result

• Added rows exist only in the new file, Removed rows only in the old one.
• Modified rows exist in both but differ, and the changed part is highlighted, so you see at a glance that only the price changed.
• Use Previous and Next to jump between changes, and Collapse unchanged lines to hide everything that stayed the same in a long file.
• Switch between Side by side and Unified view, whichever is easier to read.

Merging changes

Each change can be copied across with Move to Right or Move to Left, for example to take one colleague’s corrections but not another’s. Undo change takes a step back, and Download saves the merged file as CSV, ready to open in your spreadsheet again.

Tips for clean results

• Remove columns that change every time, such as “last updated” timestamps, before exporting, or every row will look modified.
• Make sure numbers use the same format in both files: 1,000.00 and 1000 look different as text.
• Very large sheets: filter to the part you care about, or split the file, if a side is larger than the limit shown above the tool.

Are my files uploaded?

Unlike our other tools, File Comparison sends the two texts to our server, which works out the differences and sends the result back. They’re processed in memory and are not stored or logged. Even so, don’t paste passwords or other secrets into any online tool.

Frequently asked questions

Can I compare .xlsx files directly?

No. Save both as CSV first, as described above; that also makes the comparison faster and the result easier to read.

Does it compare cell by cell?

It compares row by row, and within a changed row it highlights exactly which part changed, which in practice shows you the changed cells.

Can I compare other kinds of files?

Yes: text, code, JSON, XML and many more. See how to compare two files online.