What is the XLSX file format?
Files with the .xlsx extension contain spreadsheets compressed in a ZIP archive, stored in an open format based on XML - Office Open XML (OOXML). The format was introduced with Microsoft Office 2007, designed to provide greater portability and interoperability than the older .xls binary format.
An .xlsx spreadsheet may contain:
- Data stored in the form of tables
- Charts and graphs
- Formulas and functions
- Named ranges, pivot tables, and conditional formatting
.xlsx is the native format for Microsoft Excel 2007 and all newer versions, and is also supported across other spreadsheet applications. It does not support macros - for workbooks that include VBA macros, the file must be saved as .xlsm, a variant of the same OOXML package. A binary-compressed alternative, .xlsb, offers smaller file sizes and faster loading for very large workbooks.
Under the hood, an .xlsx file is a standard ZIP package containing a set of XML files organized in a defined folder structure, with xl/workbook.xml as the primary entry point and [Content_Types].xml at the root.
Beyond the native Microsoft Excel application, .xlsx files are widely supported - Google Sheets and Excel for the web both allow you to browse, edit, and create .xlsx files completely free of charge.
Security & safety
RISK: LOWPlain XLSX cannot contain macros, so a .xlsx attachment is much safer than an .xlsm or legacy .xls. The remaining risks are external links and DDE/formula-based attacks: a workbook can pull data from a URL or trigger external content, so Excel opens internet/email files in Protected View - leave it on and don't enable editing for files you didn't expect. If a "spreadsheet" arrives as .xlsm and asks you to enable macros, be suspicious. Opening in Google Sheets or LibreOffice avoids Excel's VBA engine entirely.
Format details
in a nutshellPrograms that open XLSX files
Windows3 apps
LibreOffice Calc
Open-source Free, full-featured. Double-click to open; Save As to keep XLSX or export PDF/CSV. 
WPS Office Spreadsheets
Freemium Free Excel-like app (formerly Kingsoft); opens and edits XLSX with high compatibility. 
macOS3 apps
Linux2 apps
Android1 app
Google Sheets
Free Upload to Google Drive and open with Google Sheets; download back as XLSX, PDF or CSV. Technical details
deep spec| Container format | ZIP/OPC package (Open Packaging Conventions) |
| Primary markup language | XML (Extensible Markup Language) |
| MIME type | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet |
| Magic bytes (hex) | 50 4B 03 04 - standard ZIP local file header |
| Primary workbook entry | xl/workbook.xml within the ZIP package |
| Macro support | None; VBA macros require the .xlsm variant |
| Maximum rows per sheet | 1,048,576 (2^20) |
| Maximum columns per sheet | 16,384 (2^14, columns A through XFD) |
| Compression algorithm | Deflate (ZIP) applied to all XML part streams |
| Shared strings table | Repeated text values deduplicated in xl/sharedStrings.xml |
| Cell styles storage | Number formats, fonts, fills, and borders defined in xl/styles.xml |
| Encryption support | AES-256 password encryption via OOXML Encryption Info structure |
| Formula support | 400+ built-in worksheet functions; supports array formulas and structured table references |
| Standardization body | ECMA International (ECMA-376) and ISO/IEC (ISO/IEC 29500) |
| Released | 2007 (Excel 2007); standardised as ECMA-376 / ISO-IEC 29500 (2008) |
| Open standard | Yes · royalty-free |
| Specification | learn.microsoft.com |
XLSX conversions
Community Q&A
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