Convert XLS to XLSX Online
XLS is the old binary Excel format from the 1990s. Converting to XLSX gives you the modern open XML format that works with Excel 365, Google Sheets, and LibreOffice Calc.
Our converter handles all XLS files from Excel 97/2000/2003 and produces fully compatible XLSX output.
XLS is the legacy Excel format from 1997-2003; XLSX is the modern XML-based format introduced with Excel 2007. Upgrading an old XLS to XLSX gives you smaller files, far higher row and column limits, and full compatibility with current Excel, Google Sheets, and LibreOffice. This guide explains what you gain, what is preserved, and how to convert in the browser.
What is XLS?
XLS is Microsoft Excel's older binary spreadsheet format used in Excel versions before 2007. It has a 65,536 row limit and uses an older binary encoding.
XLS files have an outdated row limit, less compatibility with modern applications, and binary encoding that can cause issues with non-Microsoft software.
What is XLSX?
XLSX uses the Office Open XML standard, stores data as XML in a ZIP archive, supports over 1 million rows, and is fully compatible with all modern spreadsheet applications.
Converting XLS to XLSX removes the old row limit, improves compatibility, and makes your spreadsheets ready for modern collaborative workflows.
What You Gain by Upgrading to XLSX
| Property | XLS (legacy) | XLSX (modern) |
|---|---|---|
| Rows per sheet | 65,536 | 1,048,576 |
| Columns per sheet | 256 | 16,384 |
| File size | Larger (binary) | ~75% smaller (zipped XML) |
| Corruption recovery | Poor | Much better |
| Modern features (slicers, new charts) | No | Yes |
| Compatibility | Aging; some tools dropping support | Current standard everywhere |
What Is Preserved in the Conversion
XLS to XLSX is a faithful upgrade: cell values, formulas, multiple worksheets, formatting, charts, and named ranges all carry over. Because XLSX is a superset of what XLS could store, nothing is lost in the direction from old to new. The only thing to watch is very old macros (the legacy XLM macro language), which should be reviewed after conversion. For everyday spreadsheets, the upgrade is lossless and the file simply becomes smaller and more capable.
Why Convert XLS to XLSX?
Modern Compatibility
XLSX works perfectly with Excel 365, Google Sheets, LibreOffice Calc, and Numbers.
More Rows
XLSX is the standard format for sharing spreadsheets with colleagues on any platform.
Better Collaboration
XLSX is the standard format for sharing spreadsheets with colleagues on any platform.
Open Standard
XLSX is an ISO standard format with long-term support guaranteed.
How to Convert XLS to XLSX
Upload XLS
Select your old XLS file.
Choose XLSX output
Select XLSX as your output format.
Convert
Click convert to modernize your spreadsheet.
Download XLSX
Save your modern XLSX file.
Convert in the Browser, No Upload
The FileFormer document converter upgrades XLS to XLSX directly in your browser, keeping formulas, formatting, and every worksheet. Because it runs on your device, the spreadsheet, which may contain financial or personal data, is never uploaded to a server.
Ready to Convert XLS to XLSX?
Use our free online converter. No signup, no watermarks, practical limits.
Convert XLS to XLSXPro Tips
Check formulas after conversion
Verify that all formulas work correctly after conversion, especially complex ones.
Check charts and formatting
Review charts and conditional formatting to ensure they converted accurately.
Update your default format
Set Excel to save as XLSX by default in Excel Options.
Frequently Asked Questions
What is the difference between XLS and XLSX?
XLS is the older binary format with 65,536 row limit. XLSX is the modern XML format with 1,048,576 row limit and better compatibility.
Will all my formulas work in XLSX?
Yes, all standard Excel formulas transfer correctly to XLSX format.
Does Google Sheets support XLS?
Google Sheets can open both XLS and XLSX. XLSX generally has better compatibility.
Can I open XLSX in old Excel?
Excel 2007 and later open XLSX natively. Excel 2003 needs the Microsoft Office Compatibility Pack.
Does converting XLS to XLSX change any data?
No, all data, formulas, and formatting are preserved. XLSX is a format upgrade, not a data change.
Will I lose any data converting XLS to XLSX?
No. XLSX can store everything XLS held, so values, formulas, formatting, charts, and multiple sheets all carry over. Only very old XLM-style macros need a review afterward.
Why is my XLSX so much smaller than the XLS?
XLSX stores the workbook as zipped XML, which compresses far better than the old binary XLS. A typical spreadsheet drops to roughly a quarter of its former size with no loss of content.