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Document Format

XLSX

Excel Spreadsheet (Open XML)

XLSX is the modern Microsoft Excel spreadsheet format used by Excel 2007 and later. It's an open standard (ISO/IEC 29500) based on XML, making it readable by multiple applications — Google Sheets, LibreOffice Calc, Apple Numbers, and more. Understanding XLSX helps you work more effectively across applications and troubleshoot compatibility issues.

What is XLSX?

XLSX is part of the Office Open XML (OOXML) format family, the same framework that includes DOCX (Word) and PPTX (PowerPoint). Like DOCX, an XLSX file is actually a ZIP archive containing XML files — rename it to .zip and open it to see the internal structure: xl/worksheets/sheet1.xml (cell data), xl/styles.xml (formatting), xl/sharedStrings.xml (text cell values), xl/workbook.xml (workbook structure), xl/charts/ (chart definitions), etc. XLSX replaced the older XLS binary format (used in Excel up to 2003) in Excel 2007. XLS was a complex, proprietary binary format; XLSX is documented in a public standard with implementations available for every programming language (Python: openpyxl, pandas; JavaScript: SheetJS; Java: Apache POI; C#: EPPlus). XLSX supports: up to 1,048,576 rows and 16,384 columns per sheet (vs. 65,536 rows in XLS), multiple worksheets in one workbook, pivot tables and pivot charts, formulas with a full function library (1,000+ functions), conditional formatting, data validation, named ranges, macros (as VBA code in xlsm variant), and charts. File size: XLSX is typically much smaller than equivalent XLS due to XML compression inside the ZIP container. A spreadsheet that's 5 MB as XLS may be 500 KB as XLSX.

XLSX pros and cons

Advantages

  • Open standard — ISO/IEC 29500 published specification
  • Supported by Excel, Google Sheets, LibreOffice, Numbers, and more
  • Smaller file sizes than older XLS format
  • Large row/column limits (1M+ rows)
  • Programmatically readable with open-source libraries
  • Supports all modern Excel features including pivot tables

Limitations

  • Complex Excel features (VBA macros, some chart types) may not transfer correctly to other apps
  • Google Sheets and LibreOffice don't support all Excel formula functions
  • Advanced formatting may look different in non-Excel applications
  • Macro-enabled XLSX (XLSM) requires allowing macros — security consideration
  • Very large XLSX files can be slow to open and edit

When should you convert XLSX files?

Convert XLSX to CSV for importing data into databases, analysis tools, or systems that don't accept XLSX. Convert XLSX to PDF for sharing the spreadsheet as a fixed-layout document that looks identical for all recipients. Convert XLSX to Google Sheets format (by uploading to Google Drive) for collaborative editing without Microsoft 365. Keep XLSX when collaborating with Excel users or when using Excel-specific features like complex macros, pivot tables, or data connections.

Convert XLSX files

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XLSX FAQ

Can I open XLSX without Microsoft Excel?
Yes. Google Sheets opens XLSX files from Google Drive with excellent compatibility. LibreOffice Calc (free, open-source, Windows/Mac/Linux) opens XLSX with good compatibility — some advanced Excel features may not transfer. Apple Numbers (Mac/iPad, free) opens XLSX with reasonable compatibility for simpler spreadsheets. Microsoft Excel Online (free at office.com) opens and edits XLSX without installing anything.
What's the difference between XLSX and XLS?
XLS: Excel's binary format used in Excel 97–2003. Proprietary, harder to parse programmatically, max 65,536 rows. XLSX: Excel's Open XML format since Excel 2007. Open standard, smaller file sizes, max 1,048,576 rows. Always use XLSX unless you specifically need to support Excel 2003 or earlier — XLSX is universally better.
What is XLSM?
XLSM is XLSX with macros enabled — the 'M' stands for macro. XLSX files technically don't run macros; XLSM files contain VBA code that runs when you open the file (after you grant permission). If you receive an XLSM file, it contains executable VBA code — be cautious with XLSM files from unknown sources as macro viruses are a real threat.

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