What’s The Difference Between .Xls And .Xlsx Spreadsheet File Formats?

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In the world of electronic spreadsheets, Microsoft Excel has established itself as a foundational tool used by individuals and businesses to analyze data, manage records, and perform financial calculations. Among Excel’s various file formats, XLS and XLSX are the most commonly used, each with unique characteristics, advantages, and limitations. This article delves into the differences between these two formats to help users understand which format might be best suited for their needs.

1. Historical Context and Compatibility

  • XLS: This is the default file format for Excel versions 97 through 2003. XLS files are based on Microsoft’s Binary Interchange File Format (BIFF) and use a proprietary binary format to store information. Due to their binary nature, XLS files can only be fully opened by applications that specifically support their format, which primarily includes versions of Microsoft Excel.
  • XLSX: Introduced with Microsoft Excel 2007 as part of the Office Open XML (OOXML) standard, XLSX is the default format for all later versions of Excel. This format uses XML (Extensible Markup Language) for content, ZIP compression to reduce file size, and a structured storage system for managing document components such as worksheets and styles.

2. Structure and Storage

  • Storage of Data: XLS files store data in a binary format which encapsulates information in a compact manner, thus sometimes resulting in smaller file sizes when dealing with large amounts of data. In contrast, XLSX files use a plain text XML structure which can be larger but is easier to recover and more transparent for data processing by third-party applications not using Excel.
  • ZIP Compression: XLSX files benefit from ZIP compression, which not only reduces the file size but also organizes the data into separate files and folders within the ZIP archive. This arrangement allows for better data management and recovery, especially in cases of file corruption.

3. Security and Recovery

  • Corruption Recovery: XLSX files are generally more robust against corruption. Due to their structure, parts of the file can often be salvaged if corruption occurs. On the other hand, corruption in an XLS file often renders the entire file unusable because the data is interwoven and stored in a binary format.
  • Password Protection and Encryption: Both XLS and XLSX formats support password protection and encryption, but XLSX offers stronger encryption options, which were enhanced with the introduction of Office 2010 and later versions.

4. Functionality and Features

  • Feature Support: With the launch of Excel 2007, Microsoft expanded the capabilities of Excel, including increased limits for rows and columns, and richer conditional formatting. Many of these features are only fully supported in the XLSX format.
  • Macros and Scripting: Both formats support macros. However, if you save a workbook with macros in the XLSX format, you must change the extension to XLSM. The XLS format inherently supports macros without changing the file extension.

5. Compatibility with Other Applications

  • Cross-application Compatibility: XLSX files are based on a standard XML schema, making them more accessible for other applications to read and modify. Many non-Microsoft products offer better support for XLSX due to its open standard format.
  • Backward Compatibility: Microsoft offers compatibility packs for older versions of Excel to open XLSX files. Conversely, newer versions of Excel can open and convert XLS files with relative ease.


The choice between XLS and XLSX formats depends on the user’s needs. For those working with large datasets, requiring robust data recovery, and using software beyond older versions of Microsoft Excel, XLSX is generally the better choice. It offers improved security features, potential for reduced file sizes through compression, and better compatibility with third-party applications.

However, for users with a need for compatibility with older software or specific legacy systems that only support the XLS format, continuing to use XLS may be necessary. Understanding these differences can help users select the appropriate file format for their specific tasks and ensure that their data is stored efficiently and securely.

Shakes Gilles

Shakes covers stories ranging from science to health, to technology, to astronomy, etc... On a typical weekend, you'll find him enjoying a picnic at a local park or playing soccer with friends.