About the XLS to XLSX Online Free Tool

The XLS to XLSX Online Free Tool converts the old binary Excel format into the modern XML-based .xlsx, keeping cell values, formulas, formatting, and multiple worksheets.

Conversion runs on the IO Tools server using LibreOffice, the same engine behind most open-source document pipelines. Uploaded files are converted and deleted immediately; they are never stored or shared.

The old .xls format caps out at 65,536 rows and 256 columns. Converting to .xlsx lifts that to over a million rows, and removes the compatibility warnings modern Excel shows.

This tool has no in-browser mode. A browser has no office engine of its own, so if the server is unavailable the tool says so plainly rather than producing a poor imitation.

How to Use XLS to XLSX Online

1. Choose an .xls or .xlt file.
2. Convert it to XLSX.
3. Download the converted workbook.

What Carries Over

Data and structure are preserved:
- All worksheets, cell values, formulas, number formats, and cell styling transfer.
- Charts and conditional formatting carry over in most workbooks.
- VBA macros do not. An .xlsx cannot hold macros by design; save as .xlsm in Excel if you need them.

Common Use Cases

• Modernising old financial records or data exports so they open without warnings.
• Lifting a legacy workbook past the 65,536-row limit of the old format.
• Preparing a spreadsheet for a system or API that accepts only XLSX.

Quick FAQ

Will my original file be changed?
No. The XLSX is generated as a separate file.

Are files uploaded?
Yes. Reading the binary .xls format needs a spreadsheet engine a browser does not have, so the file is sent to the IO Tools server, converted with LibreOffice, returned, and deleted immediately.

Do my formulas still work?
Yes. Formulas are converted rather than flattened to values, so the workbook stays live. Very old or Excel-specific functions can occasionally need review.

Are all worksheets kept?
Yes. Every sheet in the workbook is converted, in the original order.