XLS vs XLSX
A detailed comparison of Excel Spreadsheet (Legacy) and Excel Spreadsheet — file size, quality, compatibility, and which format to choose for your workflow.
Excel Spreadsheet (Legacy)
Spreadsheets & DataXLS 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 While superseded by XLSX, it remains common in archived data and older business systems.
About XLS filesExcel Spreadsheet
Spreadsheets & DataXLSX is the modern Microsoft Excel format based on Open XML. It is the industry standard for spreadsheets, supporting formulas, charts, pivot tables, and conditional formatting.
About XLSX filesStrengths Comparison
XLS 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.
XLSX Strengths
- Much smaller than legacy .xls files thanks to ZIP + XML.
- Human-readable structure — easy to extract data programmatically.
- Supports macros (as .xlsm variant), charts, pivot tables, conditional formatting.
- Universal support: Excel, LibreOffice, Google Sheets, Numbers, pandas.
- ISO/IEC 29500 standardized.
Limitations
XLS 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.
XLSX Limitations
- Macros in .xlsm are a common malware vector — disabled by default in Office.
- 1M-row limit is a cultural problem — people put too much data in Excel.
- Subtle formula differences between Excel, LibreOffice, and Sheets.
- Large files with many formulas recalculate slowly.
Technical Specifications
| Specification | XLS | XLSX |
|---|---|---|
| MIME type | application/vnd.ms-excel | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet |
| Max rows | 65 536 (Excel 97-2003) | 1,048,576 |
| Max columns | 256 (A to IV) | 16,384 |
| Container | OLE Compound File | ZIP (Office Open XML) |
| Successor | .xlsx (2007) | — |
| Released in | — | Microsoft Office 2007 |
| Variants | — | .xlsx, .xlsm (macros), .xlsb (binary) |
Typical File Sizes
XLS
- Simple budget (1 sheet) 30-60 KB
- Multi-sheet financial model 500 KB - 5 MB
- Data export with 65 000 rows 5-20 MB
XLSX
- Small budget spreadsheet 20–80 KB
- Financial model with charts 1–10 MB
- Large dataset (100k rows) 10–50 MB
- Enterprise model (1M+ rows) 100–500 MB
Ready to convert?
Convert between XLS and XLSX online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
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.