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)

A Brief History of Excel File Formats

Understanding where these formats came from helps explain why both still exist today.

1985 — Microsoft Excel 1.0 launches on Macintosh with its own binary file format.
1987 — Excel 2.0 arrives on Windows. The .xls extension becomes standard.
1993 — Excel 5.0 introduces Visual Basic for Applications (VBA), enabling macros within XLS files.
1997 — Excel 97 refines the binary format. This version of XLS (BIFF8) becomes the most widely used and remains the basis of the .xls format through Excel 2003.
2006 — Microsoft announces the Office Open XML (OOXML) standard and submits it for international standardization.
2007 — Excel 2007 ships with XLSX as the default format. Row limits jump from 65,536 to over one million.
2008 — OOXML is approved as an ISO/IEC standard (ISO 29500), making XLSX a recognized open format.
Present — XLSX is the universal default. XLS persists mainly in legacy systems and archived files.

Why Did Microsoft Create XLSX?

Larger capacity - Modern data needs exceeded XLS limits
Smaller files - ZIP compression reduces size significantly
Open standard - Easier for other software to read/write
Better security - XML format is easier to scan for threats
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.

When to Use XLSM (Macro-Enabled Workbooks)

If your spreadsheet relies on VBA macros, neither XLS nor XLSX is the right choice. XLSX deliberately strips macros for security, and while XLS supports macros, its other limitations make it a poor option for new work. That is where XLSM comes in.

What is XLSM?

XLSM is identical to XLSX in structure — it uses the same XML-based, ZIP-compressed format and has the same row, column, and file size characteristics — but it allows VBA macro code to be stored inside the file.

When you should use XLSM:

Your workbook contains VBA macros or user-defined functions
You need automation like auto-generated reports, data validation scripts, or custom toolbar buttons
You are distributing templates that include macro-driven workflows

Security considerations:

Most email providers and corporate firewalls block or flag XLSM attachments because macros can carry malicious code
Recipients will see a security warning when opening an XLSM file and must explicitly enable macros
If your recipients only need to view the data (not run macros), export a copy as XLSX or PDF before sharing

Quick rule of thumb: Use XLSX for data and XLSM for automation. If you are unsure, start with XLSX and switch to XLSM only when you add your first macro.

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:

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

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

XLSX to XLS

In Excel:

Open the .xlsx file
Click File → Save As
Choose "Excel 97-2003 Workbook (*.xls)"
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 in your browser
Linkyhost XLS Viewer - View legacy XLS files online
Google Sheets - Full editing (free)
LibreOffice Calc - Full editing (free software)

Convert to PDF

For sharing without editing:

Upload to Linkyhost Excel to PDF
Get a shareable link
Formatting preserved perfectly

How to Share Excel Files

Sharing an Excel file by email attachment often leads to formatting issues, version conflicts, and file size limits. Here are better approaches.

Convert to PDF first: If the recipient only needs to read the data, converting to PDF guarantees the layout stays intact regardless of what software they use. Use Linkyhost Excel to PDF to convert and generate a shareable link in one step.

Use cloud storage: Upload to Google Drive, OneDrive, or Dropbox and share a link. This avoids attachment size limits and lets you control permissions.

Share via Google Sheets: Upload your XLS or XLSX file to Google Sheets, then share the link. Recipients can view without installing any software, and you can set view-only or edit permissions.

Best practices for sharing:

Remove sensitive data or hidden sheets before sharing
Use PDF when recipients do not need to edit
Use cloud links when you want to update the file after sharing
Include a brief description of what each sheet contains if the workbook has multiple tabs

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.

Performance Tips for Large Excel Files

Working with spreadsheets that contain tens of thousands of rows or complex formulas can be slow regardless of file format. These tips help keep things responsive.

Reduce file size:

Delete unused rows and columns beyond your data range — Excel sometimes tracks empty cells far beyond the actual content area
Compress or remove embedded images; link to external images where possible
Clear formatting on cells that do not need it, especially conditional formatting rules that span large ranges

Speed up calculations:

Switch calculation mode to Manual (Formulas → Calculation Options → Manual) while editing, then recalculate with Ctrl+Shift+F9 when ready
Replace volatile functions like INDIRECT, OFFSET, and NOW with static alternatives where possible
Use helper columns instead of deeply nested formulas — they are easier to debug and often faster to calculate

Use the right format:

For very large files that do not need to be shared outside Excel, consider XLSB (Excel Binary Workbook). It offers the speed of binary with the capacity of XLSX.
Avoid keeping files in XLS format if they are near the 65,536 row limit — convert to XLSX to prevent truncation

Hardware and settings:

Disable automatic spell-checking on large workbooks (File → Options → Proofing)
Close other workbooks while working with a large file to free memory
Keep Excel and your operating system updated for the latest performance improvements

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

Frequently Asked Questions

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.

Is XLSB better than XLSX for performance?

XLSB (Excel Binary Workbook) loads and saves faster than XLSX, especially for very large files. However, XLSB is not an open standard, so it has weaker support outside of Excel. Use XLSB for internal workbooks that stay within Excel, and XLSX when you need to share files or work with other applications.

How do I open an XLS file without Excel on my phone?

On Android, Google Sheets opens XLS files natively. On iPhone, the Numbers app handles XLS files, or you can install the free Microsoft Excel app. For a quick view without installing anything, open the Linkyhost XLS Viewer in your mobile browser and upload the file.

Can I password-protect an XLSX file?

Yes. In Excel, go to File → Info → Protect Workbook → Encrypt with Password. This works for both XLSX and XLS files. Keep in mind that if you forget the password, recovery is extremely difficult. For sharing a read-only version, consider converting to PDF using Linkyhost Excel to PDF instead.

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.