The legacy binary format for Microsoft Excel spreadsheets (97-2003)
XLS is the legacy binary file format used by Microsoft Excel for spreadsheets from Excel 97 through Excel 2003. Before being replaced by the XLSX format in Excel 2007, it was the standard format for Excel spreadsheets and became widely used in business, finance, science, and many other fields.
XLS files can store various types of data including text, numbers, formulas, macros, charts, and formatting information. The format uses a proprietary binary structure known as Binary Interchange File Format (BIFF), making it challenging to work with outside of Microsoft's applications.
Despite being officially superseded by XLSX, the XLS format continues to be used in many organizations, particularly in environments with older software or established systems that were built around this format. It remains supported in modern versions of Excel and other spreadsheet applications for backward compatibility.
XLS files use a complex binary structure based on the Compound File Binary Format (similar to a mini file system). The format stores workbooks containing one or more worksheets, along with formulas, functions, charts, macros (in VBA), and various formatting information. Its binary nature made it efficient for the computing resources of its era but created challenges for interoperability and long-term data preservation.
XLS remains essential in environments using older versions of Microsoft Office (pre-2007) or legacy systems built around this format. Many enterprise applications, particularly in finance, healthcare, and government sectors, were designed to work specifically with XLS files and haven't been updated to support newer formats.
Organizations with established spreadsheet templates, macros, and procedures built for XLS often continue using this format to avoid disrupting workflows. Converting complex spreadsheets with extensive macros and custom functionality to newer formats can be challenging and costly, leading many businesses to maintain XLS compatibility.
Some organizations distribute spreadsheets with VBA macros in XLS format because the macro behavior is well-understood and consistent in this format. While XLSM (the macro-enabled variant of XLSX) is now preferred for new development, legacy macros sometimes function more predictably in XLS.
For simple spreadsheets where the larger data capacity of XLSX isn't needed, XLS can serve as a compact format for data exchange. Some users prefer XLS for smaller datasets because the files open quickly in most applications without the overhead of processing and uncompressing XML content.
Historical spreadsheets from the 1990s and early 2000s are often archived in XLS format. While not ideal for long-term preservation, many organizations maintain archives of XLS files that represent important historical data and calculations from earlier periods.
XLS is supported across Microsoft Office versions:
Many non-Microsoft applications support XLS files:
Various libraries can work with XLS files:
XLS files can be used across various platforms:
| Feature | XLS | XLSX | CSV | ODS | |
|---|---|---|---|---|---|
| File Format | |||||
| Row Limit | |||||
| Column Limit | |||||
| Formatting | |||||
| Formulas | |||||
| Macros | |||||
| Open Format | |||||
| File Size |
XLS offers good legacy compatibility and strong macro support but has significant limitations in data capacity compared to XLSX. CSV provides maximum simplicity and interoperability but lacks formatting and calculation capabilities. ODS offers an open standard alternative with good features, while PDF excels at layout preservation but sacrifices editability.
When converting from XLSX to XLS, be aware of the row and column limitations (65,536 rows and 256 columns). Any data beyond these limits will be truncated. Some newer features like slicers, timelines, and certain chart types aren't supported in XLS. Use "Save As" in Excel and select "Excel 97-2003 Workbook (*.xls)" format. Review the compatibility checker warnings to identify potential issues.
Converting from CSV to XLS is generally straightforward. Import the CSV file into Excel or another spreadsheet application, then save as XLS format. Pay attention to text encoding, especially for international characters. For date and number formatting, you may need to manually adjust formats after import as CSV doesn't store this information. Consider using Excel's Text Import Wizard for more control over the import process.
When converting from OpenDocument Spreadsheet (ODS) to XLS, use LibreOffice or OpenOffice's "Save As" function. Complex formatting and some functions may not translate perfectly. Charts and graphics typically convert well, but check for positioning issues. Macros in ODS won't convert to VBA automatically and will need to be rewritten.
Converting XLS to XLSX generally works well and allows you to take advantage of newer Excel features and larger data capacity. Open the file in a recent version of Excel and use "Save As" to select the XLSX format. Most formatting, formulas, and basic macros will convert successfully, though you may need to review and update complex VBA code that interacts with Excel's object model.
When converting XLS to CSV, remember that you'll lose all formatting, multiple worksheets, formulas (only values will be preserved), and any charts or graphics. Each worksheet must be saved as a separate CSV file. Use "Save As" and select "CSV (Comma delimited) (*.csv)" format. For international characters, pay attention to the encoding options. Consider creating a copy of your XLS file before conversion to preserve the original.
Converting XLS to PDF creates a fixed-layout document that preserves the appearance but removes editability. Use the "Export to PDF" or "Save As PDF" function in your spreadsheet application. Set print areas appropriately before conversion to control what appears on each page. Consider page orientation, scaling options, and whether to include gridlines and headers. For multi-sheet workbooks, specify whether to convert all sheets or only active ones.