XLS to XLSX Converter

Description

Convert XLS into XLSX, keeping the same spreadsheet structure and formatting while changing the underlying file format. XLSX is the current default format, so this is typically an upgrade from the older XLS format rather than a lateral move.

Use Cases

  • Upgrading an old XLS file so it opens correctly in current software without a compatibility warning.
  • Shrinking file size for storage or email - XLSX's ZIP-based container compresses meaningfully better than XLS's.

Format Comparison

FeatureXLSXLSX
CompressionNoYes (ZIP container)
LayoutPreserved (styles, structure)Preserved (styles, structure)
Format eraLegacy (pre-2007)Modern (2007+)

Example Workflow

  1. Upload your XLS file.
  2. Click “Convert to XLSX.”
  3. Download the resulting XLSX file.

Complete Guide to XLS to XLSX Conversion

What is XLS to XLSX Conversion?

Transforms legacy Excel (XLS) files into modern Excel (XLSX) format, upgrading binary spreadsheet files to the OpenXML format with enhanced features, better compression, and Office 365 compatibility.

Why Choose XLSX?

  • Modern OpenXML format with superior compression
  • Advanced Excel features and functions
  • Full Office 365 and Excel Online compatibility
  • Support for large datasets and complex formulas
  • Enhanced charts, pivot tables, and data analysis tools

Technical Specifications

AspectXLS FormatXLSX Format
File TypeBinary spreadsheetOpenXML spreadsheet
CompatibilityExcel 97-2003Excel 2007+
File SizeLarger binary formatCompressed XML format
Cloud SupportLimitedOffice 365, Excel Online

Best Practices

Before Conversion
  • Test formulas and calculations
  • Check for Excel-specific features
  • Verify data integrity
  • Document any custom macros
  • Create backup of original XLS file
After Conversion
  • Verify formulas work in modern Excel
  • Test advanced Excel features
  • Apply modern Excel styles and themes
  • Optimize for cloud collaboration
  • Test with Excel Online and mobile apps
Conversion Stats
  • Success Rate: 98%
  • Avg Processing: 1–3 seconds
  • Max File Size: 25MB
  • Formula Compatibility: Excellent
XLSX Format Benefits
  • ✓ Modern Excel compatibility
  • ✓ Advanced data analysis
  • ✓ Cloud collaboration
  • ✓ Better compression
Related Tools

About XLS and XLSX

XLS (Microsoft Excel 97-2003 Workbook) is Excel's legacy binary format, still common on older systems though superseded by XLSX.

XLSX (Microsoft Excel Workbook (Office Open XML)) is Excel's modern XML-based format, supporting formulas, multiple sheets, charts, and conditional formatting.

What to expect: XLS and XLSX support similar formatting, so most content and structure should carry over cleanly.

Related Conversions

XLSX to XLS XLS to DOC XLS to DOCX XLS to ODT XLS to RTF XLS to PDF

Frequently Asked Questions

Yes. Your file is processed on our servers to perform the XLS-to-XLSX conversion, and the download link is private to your session — it isn't published or indexed anywhere.

No. The XLS to XLSX conversion runs entirely in your browser and on our servers — nothing to download or install.

Yes, files up to 51MB are supported for XLS to XLSX conversion.

Most formatting carries over cleanly for standard documents. Files with heavy custom formatting, macros, or unusual layout may need a quick manual check after conversion, since XLS and XLSX don't support identical feature sets.

No signup, no account, and no payment required to convert XLS to XLSX.