XLS vs XLSX: What's the Difference?

If you work with Excel files, you've probably seen both .xls and .xlsx file extensions. They're both Excel formats, but there are important differences.

Need to view an Excel file? Open XLS or XLSX files instantly in your browser with the LinkyHost XLSX Viewer — no Excel required.

Quick Comparison

Feature	XLS	XLSX
Introduced	1987 (Excel 2.0)	2007 (Excel 2007)
Format type	Binary	XML-based (Open XML)
Max rows	65,536	1,048,576
Max columns	256 (IV)	16,384 (XFD)
File size	Larger	Smaller (compressed)
Security	Less secure	More secure
Compatibility	Older software	Modern software

What is XLS?

XLS is the original Excel Binary File Format used from Excel 97 to Excel 2003. It stores data in a proprietary binary format.

Characteristics:

• Binary format (not human-readable)
• Smaller row/column limits
• Can contain macros
• Supported by all Excel versions

What is XLSX?

XLSX is the modern Excel format introduced in 2007. The "X" stands for XML - it's actually a compressed ZIP file containing XML documents.

Characteristics:

• XML-based (technically readable)
• Much larger capacity
• Cannot contain macros (use XLSM for macros)
• Smaller file sizes due to compression
• Open standard (Office Open XML)

Why Did Microsoft Create XLSX?

1. Larger capacity - Modern data needs exceeded XLS limits
2. Smaller files - ZIP compression reduces size significantly
3. Open standard - Easier for other software to read/write
4. Better security - XML format is easier to scan for threats
5. Data recovery - XML is easier to repair if corrupted

Which Format Should You Use?

Use XLSX when:

• Creating new spreadsheets
• Working with large datasets
• Sharing files with others
• File size matters
• Using modern Excel features

Use XLS when:

• Compatibility with very old software
• Required by legacy systems
• Working with macros (though XLSM is better)

Bottom line: Use XLSX unless you have a specific reason not to.

How to Tell XLS from XLSX

By extension:

• File ends in .xls = XLS format
• File ends in .xlsx = XLSX format
• File ends in .xlsm = XLSX with macros

By file size: The same data in XLSX is typically 25-75% smaller than XLS.

By opening: XLS files may show "Compatibility Mode" in newer Excel versions.

Converting Between Formats

XLS to XLSX

In Excel:

1. Open the .xls file
2. Click File → Save As
3. Choose "Excel Workbook (*.xlsx)"
4. Save

Online: Upload to online converters if you don't have Excel.

XLSX to XLS

In Excel:

1. Open the .xlsx file
2. Click File → Save As
3. Choose "Excel 97-2003 Workbook (*.xls)"
4. Save

Warning: You may lose data if your spreadsheet exceeds XLS limits.

Opening XLS and XLSX Files

Without Excel

Free options:

• LinkyHost XLSX Viewer - Quick preview
• LinkyHost XLS Viewer - Quick preview
• Google Sheets - Full editing (free)
• LibreOffice Calc - Full editing (free software)

Convert to PDF

For sharing without editing:

1. Upload to LinkyHost Excel to PDF
2. Get a shareable link
3. Formatting preserved perfectly

File Size Comparison

Example with identical data:

Data	XLS Size	XLSX Size	Savings
1,000 rows	150 KB	45 KB	70%
10,000 rows	1.2 MB	350 KB	71%
50,000 rows	5.5 MB	1.4 MB	75%

XLSX compression is very effective, especially for text-heavy data.

Compatibility Issues

XLSX in Old Software

Old programs that only support XLS:

• Excel 2003 and earlier (without compatibility pack)
• Some legacy business software
• Old database import tools

Solution: Install Microsoft's free compatibility pack or save as XLS.

XLS in Modern Software

Most modern software opens XLS without issues:

• Excel 2007+ ✓
• Google Sheets ✓
• LibreOffice ✓
• Numbers ✓

Security Considerations

XLS Security Risks

• Binary format can hide malicious code
• Harder to scan for threats
• Macro viruses were common in XLS files

XLSX Security Benefits

• XML is transparent and scannable
• Cannot contain macros (XLSM is separate)
• Easier to detect threats
• Compression adds minor obfuscation

What About XLSM, XLSB, and Others?

Extension	Description
.xlsx	Standard Excel 2007+ workbook
.xlsm	Excel workbook with macros
.xlsb	Binary workbook (smaller, faster)
.xltx	Excel template
.xls	Legacy Excel 97-2003

FAQ

Can I just rename .xls to .xlsx?

No. The formats are completely different internally. You must convert properly using Excel or a converter.

Which is more compatible?

XLS works with older software, but XLSX works with all modern software. For most users, XLSX is more practical.

Do I lose data converting XLS to XLSX?

No, converting XLS to XLSX preserves all data. Converting XLSX to XLS may lose data if you exceed the smaller limits.

Why is my XLSX larger than XLS?

Unusual, but possible with many images or complex formatting. Generally XLSX is smaller.

Can Google Sheets open both?

Yes. Google Sheets opens and exports both XLS and XLSX.

Summary

XLS:

• Old format (1997-2003)
• 65K row limit
• Larger files
• Legacy compatibility

XLSX:

• Modern format (2007+)
• 1M+ row limit
• Smaller files (compressed)
• Better security

Recommendation: Use XLSX for new files. Convert old XLS files to XLSX when possible. Use LinkyHost to share as PDF for universal compatibility.