Spreadsheet format
What is a .xlsx file?
XLSX is the spreadsheet format of Microsoft Excel since 2007. It stores sheets, formulas, formats and charts in one file.
Inside it’s a ZIP of XML files. Google Sheets, LibreOffice and Numbers open it, though advanced features can change.
fileclay opens and writes XLSX
XLSX vs CSV vs ODS
| XLSX | CSV | ODS | |
|---|---|---|---|
| Formulas | Yes | No | Yes |
| Several sheets | Yes | No | Yes |
| Formatting | Yes | No | Yes |
| Opens in | Spreadsheet apps | Anything | Spreadsheet apps |
| Best for | Working with Excel | Moving data between apps | Open-source workflows |
When to use XLSX
Good for
- Workbooks with formulas and charts
- Sharing with Excel users
- Reports with several sheets
Not a good fit
- Importing data into other software: CSV is simpler
- Macros: they need .xlsm
- Final reports nobody should edit: use PDF
How to open .xlsx files
| Platform | App | Notes |
|---|---|---|
| Windows, macOS | Microsoft Excel | Full support |
| Any system | LibreOffice Calc | Free |
| macOS, iPhone | Numbers | Built in |
| Browsers | Excel for the web, Google Sheets | Needs an account |
Convert XLSX files
How to identify a .xlsx file
An XLSX is a ZIP, so it starts with “PK”, like DOCX, ODT and EPUB. The list of files inside is what identifies it.
50P
4BK
03
04
It’s read here, in your browser. Only the first bytes.
Your file
What comes after
[Content_Types].xmlThe list of parts
xl/workbook.xmlThe sheets
xl/worksheets/The cells
xl/sharedStrings.xmlThe text in the cells
Questions about XLSX
What is the difference between XLS and XLSX?
XLS is the old binary format, limited to 65,536 rows. XLSX is the XML-based one Excel has used since 2007.
Can I open an XLSX without Excel?
Yes. LibreOffice, Google Sheets and Numbers all open it.
Does converting XLSX to CSV lose anything?
Yes: formulas become values, formatting goes, and only one sheet is kept per file.
How many rows does an XLSX allow?
1,048,576 per sheet.