About XLS Files
Excel Spreadsheet (Legacy)
XLS is the legacy binary format for Microsoft Excel 97-2003 spreadsheets. While superseded by XLSX, it remains common in archived data and older business systems.
Family
Spreadsheets & Data
Extension
.xls
MIME Type
application/vnd.ms-excel
Can Use As
HOW XLS
CAME TO BE.
Excel 2.0 for Windows shipped in 1987 with .xls as its native binary format. An earlier Excel 1.0 had launched on Mac in 1985, but the Windows version’s timing — just ahead of the Windows 3.0 explosion — made Excel the spreadsheet that ate Lotus 1-2-3. By the mid-1990s Excel had roughly 90% market share and .xls had become the universal grammar of financial modelling.
Like .doc, .xls converted in Excel 97 to the OLE Compound File container. And like .doc, it was replaced by a ZIP+XML successor (.xlsx) in Office 2007. For two decades .xls was the file every accountant, banker, and analyst spent their career in. You still find .xls attached to emails from long-established businesses, regulators, and older government portals.
CURIOSITIES &
TRIVIA.
Excel 97 raised the row limit from 16 384 to 65 536; Excel 2007 (XLSX) exploded it to 1 048 576.
The famous "VLOOKUP" function first appeared in Excel 2.0 in 1987 and has not changed its argument order in 38 years.
Early Excel files could contain executable macros in XLM (pre-VBA) — a format attackers still use for malware because antivirus tools often miss it.
Every .xls file contains a hidden stream called "Workbook" that holds the actual cells; metadata lives in separate streams.
The maximum column count in Excel 97-2003 is 256 (A-IV) — which is why ancient CSV imports truncate at column IV.
STRENGTHS &
LIMITATIONS.
Strengths
- Universal legacy — every Excel since 1997 opens .xls natively.
- Binary format is compact and loads quickly.
- Full support for formulas, charts, pivots, and VBA macros.
- Deep integration with every accounting and ERP system of the 1990s-2000s.
Limitations
- Row/column limits are ~64× smaller than modern XLSX.
- Macro-enabled variants are a notorious malware vector.
- Binary corruption often means total data loss.
- Cannot represent modern Excel features (dynamic arrays, LAMBDA, structured references).
- Microsoft stopped evolving the format in 2007.
Typical Sizes & Weights
Simple budget (1 sheet)
30-60 KB
Multi-sheet financial model
500 KB - 5 MB
Data export with 65 000 rows
5-20 MB
Technical Specifications
- MIME type
- application/vnd.ms-excel
- Max rows
- 65 536 (Excel 97-2003)
- Max columns
- 256 (A to IV)
- Container
- OLE Compound File
- Successor
- .xlsx (2007)
CONVERT FROM
XLS
Common Use Cases
Legacy spreadsheets, data migration, older Excel files.
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Frequently Asked Questions about XLS
Frequently Asked Questions
XLS is the legacy Microsoft Excel binary format used from 1987 to 2007, storing worksheets, formulas, charts, and VBA macros. Excel 97 switched XLS to the OLE Compound File container. It was replaced as default by XLSX in Office 2007 but survives in legacy financial systems and older government databases.
XLS files open in every Excel version since 1997, Google Sheets (free), LibreOffice Calc (free), Apple Numbers, and most online viewers. The maximum worksheet size in XLS is 65 536 rows × 256 columns — modern XLSX raises those limits dramatically.
Use KaijuConverter's XLS-to-XLSX converter, or open the .xls in Excel and use Save As → Excel Workbook (.xlsx). LibreOffice and Google Sheets also convert on save. Modern XLSX supports 1 048 576 rows per sheet — 16× more than XLS.
Always XLSX for new spreadsheets. XLSX is 75% smaller, supports modern Excel features (dynamic arrays, LAMBDA functions, 1M+ rows), and is an open ISO standard. XLS is only for compatibility with pre-2007 software.
XLS files with .xlsm-style macros have been a major malware vector since the 1990s. Modern Excel blocks macros from unknown sources by default. For unknown .xls attachments, open in LibreOffice or Google Sheets first — both strip macro code during import.
Excel 97-2003 stored row numbers as 16-bit integers, capping every sheet at 65 536 rows × 256 columns. Excel 2007 switched to 20/14-bit numbering in the XLSX format, raising limits to 1 048 576 rows × 16 384 columns. Convert to XLSX to bypass the cap.