Convert XLSX to XLS — Free Online Converter
Convert Excel Open XML Spreadsheet (.xlsx) to Microsoft Excel Spreadsheet (.xls) online for free. Fast, secure document conversion with no watermarks or registration.
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How to Convert
Upload your .xlsx file by dragging it into the upload area or clicking to browse.
Choose your output settings. The default settings work great for most files.
Click Convert and download your .xls file when it's ready.
About XLSX to XLS Conversion
XLSX is the modern Office Open XML format used by Excel 2007 and later. XLS is the legacy Binary Interchange File Format (BIFF8) from Excel 97-2003. Converting XLSX to XLS downgrades a modern spreadsheet to the older binary format for compatibility with legacy systems, older software installations, and automated workflows that have not been updated to handle the newer format.
While this conversion goes against the general trend of format modernization, it remains necessary in many real-world scenarios. Industrial control systems, legacy accounting software, government systems built on pre-2007 technology, and automated import processes hardcoded to expect XLS input all require this backward-compatible format.
Why Convert XLSX to XLS?
Many industrial and enterprise systems were built before 2007 and have never been updated. ERP modules, legacy inventory management systems, and custom reporting tools that accept Excel input were often programmed specifically for the BIFF binary format. These systems cannot parse XLSX's XML structure. Converting to XLS is the only way to feed modern Excel data into these older pipelines.
Some organizations also maintain XLS as their standard for maximum backward compatibility. When spreadsheets must be opened on machines running Office 2003 or earlier (still common in manufacturing, healthcare, and government environments), converting to XLS ensures the file opens without any compatibility issues or format conversion prompts.
Common Use Cases
- Feed spreadsheet data into legacy ERP systems that only accept XLS binary format
- Share files with colleagues using Microsoft Office 2003 or earlier
- Prepare data exports for industrial control systems with hardcoded XLS import
- Generate XLS files for automated workflows that parse the BIFF binary format
- Ensure compatibility with legacy accounting and inventory management software
How It Works
The conversion engine uses LibreOffice in headless mode to parse the XLSX Open XML package and re-serialize it as a BIFF8 binary workbook. Cell values, formulas (translated from OOXML formula syntax to BIFF), number formats, cell styles, and basic chart objects are mapped to their XLS equivalents. Data exceeding XLS limits is handled gracefully: rows beyond 65,536 and columns beyond 256 (IV) are truncated with a warning.
Quality & Performance
Standard cell data and formatting convert accurately. Features exclusive to XLSX — such as tables (ListObjects), slicers, dynamic array formulas, Power Query, and icon-set conditional formatting — are either simplified or removed because they have no BIFF8 equivalent. Conditional formatting is limited to three rules per range. Charts with modern style elements may revert to classic chart styles.
Device Compatibility
| Device | XLSX | XLS |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Partial | Partial |
| Linux | Partial | Partial |
| Web Browser | No |
Tips for Best Results
- 1Check row counts before converting — data beyond row 65,536 will be silently truncated
- 2Replace dynamic array formulas with static values (paste as values) before converting
- 3Remove Excel Table formatting and convert to regular ranges before downgrading to XLS
- 4Test the XLS output in the target legacy system to verify formatting compatibility
- 5Keep the original XLSX as the master copy — the XLS is a reduced-feature derivative
Related Conversions
XLSX to XLS conversion provides backward compatibility for legacy systems that require the older Excel binary format, at the cost of modern features and expanded data limits.