Convert XLS to Excel — Free Online Converter

XLS is the legacy binary spreadsheet format from Microsoft Excel 97-2003, using the Binary Interchange File Format (BIFF8). The modern Excel format (XLSX) uses Open XML, a ZIP-compressed collection of XML files standardized as ISO/IEC 29500. Converting XLS to the modern Excel format upgrades the file from the proprietary binary structure to the open, XML-based container that current versions of Excel, Google Sheets, and LibreOffice expect.

This conversion preserves cell values, basic formulas, number formatting, column widths, and sheet names while migrating the underlying storage format. The resulting file is smaller due to ZIP compression, more resilient to corruption, and fully compatible with collaboration features in Microsoft 365 and Google Workspace.

Microsoft deprecated the XLS format with Office 2007, and modern Excel versions display a compatibility warning when opening XLS files. Features like tables, sparklines, conditional formatting rules beyond three, and worksheets with more than 65,536 rows are unavailable in the legacy format. Converting to the modern format unlocks these capabilities and removes the compatibility barrier.

Organizations maintaining archives of XLS files from the early 2000s face increasing risk as fewer applications support BIFF8 parsing. Converting to the modern format future-proofs the data while reducing file sizes by 30-50% through ZIP compression, saving storage and speeding up email attachments.

The conversion engine uses LibreOffice in headless mode to parse the XLS BIFF8 binary records, reconstruct the workbook in memory, and re-serialize it as an Open XML package. Cell values, formulas, number formats, cell styles, column widths, row heights, sheet names, and print settings are mapped to their OOXML equivalents. VBA macro code is not carried over because XLSX does not support macros — use XLSM if macros are needed.