Spreadsheet format
What is a .xls file?
XLS is the old binary spreadsheet format of Microsoft Excel, used until Excel 2003. Current spreadsheet apps still open it.
It’s limited to 65,536 rows and 256 columns, and it was replaced by XLSX in 2007. Old files are worth converting if you keep working on them.
fileclay opens and writes XLS
XLS vs XLSX vs CSV
| XLS | XLSX | CSV | |
|---|---|---|---|
| Storage | Binary | ZIP with XML | Plain text |
| Rows per sheet | 65,536 | 1,048,576 | No format limit |
| Formulas | Yes | Yes | No |
| Best for | Old workbooks | Current work | Moving data between apps |
When to use XLS
Good for
- Software that only reads the old format
- Keeping old workbooks as they are
- Sharing with very old Excel versions
Not a good fit
- New workbooks: XLSX is the current format
- Data over 65,536 rows
- Files from unknown senders: they can contain macros
How to open .xls files
| Platform | App | Notes |
|---|---|---|
| Windows, macOS | Microsoft Excel | May open in Protected View |
| Any system | LibreOffice Calc | Free |
| Browsers | Google Sheets | Needs an account |
| macOS, iPhone | Numbers | Built in |
Convert XLS files
How to identify a .xls file
XLS uses the old Microsoft compound file format, which starts with D0 CF 11 E0. Old .doc and .ppt files start the same way.
D0
CF
11
E0
It’s read here, in your browser. Only the first bytes.
Your file
Questions about XLS
Should I convert XLS to XLSX?
If you keep working on the file, yes: it has higher limits and is the current format.
Does converting XLS to XLSX lose anything?
Data and formulas carry over. Macros need .xlsm.
Why does Excel warn me when opening an XLS?
Old formats open in Protected View because they can contain macros.