XLSX is the file format of Microsoft Excel workbooks since Excel 2007. A single file can hold many sheets, each with values, formulas, formatting, charts and images. It’s an open, published standard, so Google Sheets, Apple Numbers and LibreOffice read and write it too.
What’s inside an XLSX file
An XLSX file is a ZIP archive. Rename one to .zip and you can open it and see folders of XML files: one per worksheet, one for shared text, one for styles, and others for charts and images. This design, called Office Open XML, has two practical benefits: files are compressed, and a damaged file can often be partly recovered because each part is separate.
XLSX, XLSM and XLS
| Extension | What it is |
|---|---|
.xlsx |
Standard workbook. Cannot contain macros. |
.xlsm |
Same format with macros (VBA code) allowed. |
.xls |
The older Excel 97–2003 binary format. |
XLS stored everything in one binary file and limited each sheet to 65,536 rows and 256 columns. Excel still opens it in Compatibility Mode, but some newer services and apps no longer accept it. Converting XLS to XLSX lifts the old limits and makes the file easier for other software to read.
Macros are kept out of .xlsx on purpose: a workbook ending in .xlsx can’t run code, which makes it safer to open when it comes from someone else. If a file needs macros, Excel saves it as .xlsm.
XLSX or CSV?
| XLSX | CSV | |
|---|---|---|
| Sheets | Many | One table |
| Formulas | Yes | Results only |
| Formatting | Yes | None |
| Numbers vs text | Stored explicitly | Guessed when opened |
| Readable by any software | Spreadsheet apps and libraries | Practically everything |
XLSX is better for working with data; CSV is better for moving it between systems.
Opening XLSX without Excel
- Google Sheets: upload to Google Drive and open it, or use File › Import.
- Apple Numbers: free on Mac, iPhone and iPad; opens and exports XLSX.
- LibreOffice Calc: free on Windows, Mac and Linux.
- Excel for the web: free with a Microsoft account.
Complex features such as macros, pivot table refresh and some chart types may behave differently outside Excel, but values, formulas and basic formatting carry over well.