.xlsx File Extension

What kind of file is an .xlsx?

An .xlsx file is a Microsoft Excel workbook in the Office Open XML family. It can hold multiple worksheets, formulas, cell values, styles, tables, charts, PivotTables, images, and document properties. Its registered MIME type is application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.¹

Despite the word “XML,” XLSX is not one plain-text file. It is a ZIP package containing XML parts and related resources. Unencrypted packages commonly begin with ZIP signature bytes 50 4B 03 04, but DOCX, PPTX, EPUB, JAR, and ordinary ZIP files can share that header. Reliable identification also checks package content types and relationships.¹

How do I open an .xlsx on my computer?

• On Windows or macOS, Microsoft Excel offers the most complete editing experience.
• In a web browser, Excel for the web opens common workbook features, although some desktop features behave differently or are unavailable.²
• On macOS, iPhone, and iPad, Apple Numbers can import and edit .xlsx files.³
• On Windows, macOS, and Linux, LibreOffice Calc can open and save .xlsx files.⁴

Complex formulas, charts, PivotTables, conditional formatting, fonts, hidden sheets, and external links can change between applications. Reopen an important workbook in the software your recipient will use and review the result.

Poly support for .xlsx

Poly gives compatible XLSX workbooks a thumbnail and connected spreadsheet preview. It indexes readable cell content and rendered sheets, so you can search workbook text and find visually similar pages. The Poly agent can use both the spreadsheet text and sheet images.

The interactive preview requires an internet connection. Password-protected, damaged, or unsupported workbooks may not preview or index completely. Poly does not run macros or refresh external data connections, and its preview is for reading and discovery rather than editing cells or auditing calculations.

History of .xlsx

Microsoft introduced .xlsx with Office 2007 as Excel's default XML-based workbook format. The underlying Office Open XML standard was published as the first edition of ECMA-376 in December 2006 and later became ISO/IEC 29500.⁵

The final x distinguishes the XML-based workbook from the older binary .xls convention. Microsoft defines .xlsx as macro-free: it cannot store VBA code or Excel 4.0 macro sheets. Macro-enabled workbooks use .xlsm, while .xlsb stores a newer binary workbook representation.⁶

Working with .xlsx and alternatives

Current Excel worksheets can contain up to 1,048,576 rows by 16,384 columns, though usable workbook size also depends on memory, formulas, styles, and other features.⁷ Pick a format based on what must survive:

XLSX files are macro-free, but they are not automatically safe. Packages can contain external links, embedded objects, personal information, hidden content, and ActiveX parts. Review untrusted workbooks before enabling external content, and inspect hidden sheets, comments, properties, cached data, and links before sharing.¹