Convert XLS to XLSX
The fastest way to convert Microsoft Excel Spreadsheet (Legacy) to Microsoft Excel Open XML Spreadsheet online. Free, secure, and works on any device.
1How to convert XLS to XLSX
Drag & drop your XLS file into the box above.
Click "Convert" to transform it to XLSX instantly.
Save your new file to your device.
2Why use Flux Converter?
Zero Data Usage
Files are converted in your browser. No uploading means no data usage and total privacy.
Lightning Fast
Powered by WebAssembly, conversions happen instantly on your device.
No Limits
Convert as many files as you want, of any size.
Universal
Works on Windows, Mac, Linux, Android, and iOS.
3Why convert XLS to XLSX?
Understanding the strengths and limitations of each format helps you decide when converting from XLS to XLSX makes sense. The XLS format was the standard Excel format from 1997 to 2007. It uses a proprietary binary format (BIFF) that Microsoft eventually replaced with the open XLSX format. XLSX was introduced with Microsoft Office 2007 as the successor to the binary XLS format. It uses ZIP-compressed XML for better interoperability.
XLS
XLSXTarget
4Technical Details
| Feature | XLS | XLSX |
|---|---|---|
| Full Name | Microsoft Excel Spreadsheet (Legacy) | Microsoft Excel Open XML Spreadsheet |
| MIME Type | application/vnd.ms-excel | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet |
| Category | Document | Document |
| Use Cases | Legacy system compatibility, Older Excel file migration, Simple data storage, Backward-compatible spreadsheets | Financial reports and budgets, Data analysis and dashboards, Inventory management, Scientific data recording |
| Description | XLS is the legacy binary file format used by Microsoft Excel versions 97-2003. It is widely supported but heavier than the modern XLSX format. | XLSX is the default file format for Microsoft Excel. It stores spreadsheet data in an XML-based format, supporting formulas, charts, and macros. |
5Frequently Asked Questions
What is the difference between XLS and XLSX?
XLS (Microsoft Excel Spreadsheet (Legacy)) and XLSX (Microsoft Excel Open XML Spreadsheet) serve different purposes. XLS is the legacy binary file format used by Microsoft Excel versions 97-2003. It is widely supported but heavier than the modern XLSX format. On the other hand, XLSX is the default file format for Microsoft Excel. It stores spreadsheet data in an XML-based format, supporting formulas, charts, and macros. Converting between them lets you leverage the strengths of each format depending on your needs.
Does converting XLS to XLSX lose quality?
This depends on the formats involved. For data and document formats, conversion typically preserves all content accurately. Our converter uses the best available algorithms to minimize any quality difference.
Is it safe to convert files here?
ABSOLUTELY. Unlike other sites, we do NOT upload your files to a server. All processing happens locally on your device using advanced browser technologies. Your files never leave your computer.
Is this service really free?
Yes, 100% free. No hidden fees, no watermarks, and no registration required. We support ourselves through non-intrusive advertising.
When should I use XLS instead of XLSX?
XLS is best for: Legacy system compatibility and Older Excel file migration. XLSX is better for: Financial reports and budgets and Data analysis and dashboards. Choose whichever format best fits your workflow and compatibility requirements.
Can I convert XLS on mobile?
Yes! Our converter works on iPhones, iPads, and Android devices. All processing happens in your browser — no app download needed.
Privacy Guarantee
Your files are yours. We do not store, view, or claim ownership of any content you convert. Processing is done entirely in your browser.