FormatDrop
Document Format

XLS

Microsoft Excel 97–2003 Spreadsheet

XLS is the binary spreadsheet format used by Microsoft Excel from 1997 through 2003 — the file format synonymous with spreadsheets for most of the 2000s. Like DOC and PPT, XLS was replaced in 2007 by XLSX, an open XML-based format. XLS files remain common because of the enormous volume of spreadsheets created before 2007, and because some financial systems, government databases, and enterprise software still export data in XLS format. If you work with legacy financial data, exports from old systems, or archived spreadsheets, you'll encounter XLS.

What is XLS?

XLS uses the Binary Interchange File Format (BIFF), a proprietary binary format that stores worksheet data, formulas, formatting, charts, macros, and VBA code in a structured binary file. The XLS format supports up to 65,536 rows and 256 columns per sheet — a limitation that XLSX raised to 1,048,576 rows and 16,384 columns. XLS contains all of Excel's classic features: pivot tables, charts, conditional formatting, data validation, and VBA macros. The format is replaced by XLSX (a ZIP archive of XML files) for the same reasons as DOC/DOCX: XLSX is smaller, less prone to corruption, openly documented, and better supported by third-party tools.

XLS pros and cons

Advantages

  • Universal compatibility — every spreadsheet application opens XLS
  • Preserves formulas, formatting, and charts from legacy spreadsheets
  • Supported by Excel, LibreOffice Calc, Google Sheets, Numbers, and most tools
  • Retains VBA macros for legacy automation
  • Required by some financial systems, ERPs, and legacy databases
  • Widely accepted by import utilities and data pipeline tools

Limitations

  • Limited to 65,536 rows and 256 columns per sheet
  • Binary format — not human-readable or easily parsed without libraries
  • Larger file sizes than XLSX (no ZIP compression)
  • Macros in XLS files are a malware vector
  • Actively deprecated — XLSX is the current standard
  • Some new Excel features are not available in XLS format
  • Imperfect formula compatibility with newer Excel versions in edge cases

When should you convert XLS files?

Convert XLS to XLSX to remove the row/column limit, reduce file size, and gain access to modern Excel features — open in Excel or LibreOffice and Save As → XLSX. Convert XLS to CSV for data processing pipelines, database imports, or analysis in Python/R — CSV strips formatting and formulas but is universally parseable. Convert XLS to PDF for reports you want to share without editing. Keep XLS only when a system explicitly requires it. Python pandas can read XLS: `pd.read_excel('file.xls', engine='xlrd')` (xlrd library required for .xls; openpyxl for .xlsx).

All FormatDrop conversions run entirely in your browser — no file upload, no server processing. Your files stay on your device.

XLS FAQ

What is the difference between XLS and XLSX?
XLS is a binary format used by Excel 97–2003; XLSX is a ZIP-based XML format used since Excel 2007. XLSX is smaller (ZIP compression typically saves 50–75%), supports more rows (1,048,576 vs 65,536) and columns (16,384 vs 256), is openly standardised (OOXML/ISO 29500), and less prone to corruption. XLSX separates macros into .xlsm files for security. Always use XLSX for new spreadsheets — XLS is legacy.
How do I open an XLS file on Mac?
Microsoft Excel for Mac opens XLS natively. Apple Numbers opens XLS files (File → Open). LibreOffice Calc (free) opens XLS on macOS. Google Sheets opens XLS via upload. For quick viewing, macOS Quick Look can preview XLS contents without opening an app (press Space on the file in Finder). Numbers may not preserve all Excel-specific formatting, so for important files, use Excel or LibreOffice.
Can I convert XLS to CSV without Excel?
Yes. LibreOffice Calc: open the XLS file, then File → Save As → CSV. Python pandas: `import pandas as pd; df = pd.read_excel('file.xls', engine='xlrd'); df.to_csv('output.csv', index=False)`. Google Sheets: upload XLS, then File → Download → CSV. Online converters also handle XLS to CSV. Note: CSV only preserves data and text — formulas are saved as their calculated values, and formatting is lost.
Are XLS files with macros safe to open?
Exercise caution. XLS files with VBA macros can contain malware — Excel warns you before enabling macros in untrusted files. A modern Excel setting called 'Disable all macros with notification' (the default) prevents macros from auto-running. XLS files from known senders with expected macro functionality are generally safe. If you received an unexpected XLS with a prompt to enable macros, don't enable them. Convert the XLS to XLSX or CSV to strip macros entirely.

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