What is the XL file format?
.xl is an early, now-obsolete Microsoft Excel spreadsheet file extension used during the late 1980s and early 1990s, before .xls became the standardized extension.
Files with the .xl extension are binary spreadsheets encoded in Microsoft's Binary Interchange File Format (BIFF). Depending on the Excel version that created them, the file may use an early flat BIFF2 or BIFF3 record stream, or a later OLE2 compound-file container (BIFF5/BIFF8). They store cells, formulas, numeric formats, and basic workbook structure, subject to the pre-2007 grid limit of 16,384 rows by 256 columns.
Encountering a genuine .xl file today is rare. The extension was first superseded by .xls (Excel 97-2003, BIFF8) and then by .xlsx (Office Open XML, Excel 2007 onward). A file labeled .xl is usually a legacy spreadsheet, a file whose extension was accidentally truncated, or a generic Excel file-type association placeholder set by an older application.
Modern spreadsheet applications - including current versions of Microsoft Excel, LibreOffice Calc, and Google Sheets - can generally open these files because they understand the underlying BIFF structures. If Excel refuses to open a file saved with the .xl extension, renaming it to .xls often resolves the issue, since the underlying binary format is the same.
Security & safety
RISK: MEDIUMLegacy Excel binaries can contain Excel 4.0 (XLM) or VBA macros, a known malware vector. Open unexpected .xl files in Protected View, do not enable macros unless you trust the source, and prefer a sandbox or LibreOffice for inspection.
Format details
in a nutshellPrograms that open XL files
Windows2 apps
Microsoft Excel
Paid File → Open and pick 'All Files', select the .xl. If blocked, rename a copy to .xls and open. 
LibreOffice Calc
Open-source Open the file (rename to .xls if needed); Calc reads legacy BIFF and can save as .xlsx. 
macOS2 apps
Microsoft Excel for the web / Google Sheets
Free Rename to .xls/.xlsx and upload to OneDrive (Excel online) or Google Drive (Sheets) to view. Technical details
deep spec| File type | Legacy binary Microsoft Excel spreadsheet |
| Developer | Microsoft Corporation |
| Encoding | Binary |
| Byte order | Little-endian |
| Container | OLE2/CFBF compound file (BIFF5/8) or flat BIFF record stream (BIFF2/3) |
| Encryption | Optional (legacy XOR or RC4 worksheet protection in later BIFF revisions; early files unencrypted) |
| Typical file size | 10 KB - 5 MB |
| Magic bytes | D0 CF 11 E0 A1 B1 1A E1 (OLE2 compound-file header, BIFF5/8); BOF record 09 00 or 09 02 (BIFF2/3 flat files) |
| Internal format | Binary Interchange File Format (BIFF) records: BIFF2/BIFF3 (early) through BIFF5/BIFF8 |
| Grid limit | 16,384 rows x 256 columns (pre-2007 Excel constraint) |
| MIME type | application/vnd.ms-excel |
| Successor formats | .xls (BIFF8, Excel 97-2003), then .xlsx (Office Open XML, Excel 2007 onward) |
| Associated OS | Windows, Mac OS (classic, early Excel) |
| Released | Late 1980s (early Microsoft Excel for Windows worksheet) |
| Latest version | Long superseded by .xls (BIFF8) and .xlsx (OOXML) |
| Specification | learn.microsoft.com |
XL conversions
Community Q&A
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