XLSX and XLSB are two popular Spreadsheet file formats by Microsoft Excel to store large amounts of data in Workbooks. However, the presence of formulas, user data, and objects (such as shapes) in these files can considerably increase the file size that can affect the performance of loading and saving these files. Moreover, large files consume considerable mailbox storage volume when sent via email.

This article compares the XLSX and XLSB file formats and describes how to reduce the size of Excel files for loading and saving workbooks much faster.

XLSX vs XLSB File Formats

XLSX file format is the modern-era file type of Microsoft Excel for working with workbooks. It was introduced with Microsoft Excel 2007+ and is the default file format for saving Excel workbooks. XLSX files are saved as compressed ZIP archives and are based on a combination of multiple XML files.

The XLSB files were also introduced with Microsoft Excel 2007+ and are saved in ZIP container. However, unlike XLSX and XLSM, these are compressed binary components encoded in a proprietary format.

What is the Difference between XLSX and XLSB?

So, what is the difference between XLSX and XLSB? Well, there are several differences that make these two file formats differ from each other. Primarily, these are differentiated on the basis of file format, speed, file size, and loading/saving.

Saved as a compressed archive with XML-based content inside.Saved as a compressed archive with binary encoded content inside.
XLSX files take larger space on the disc for an Excel workbook.XLSB uses considerably less space for saving the same workbook. It has been found to take 2/3rd of space as compared to the same XLSX file.
XLSX files are encoded/decoded as XML files to be saved/loaded from disc. Saving plain text files takes more time and affects the loading/saving of such files.XLSB files are saved as plain binary encoded compressed data which takes less time to save and load. On average, XLSB takes 4 times shorter than the same size XLSX file.

Well if XLSB is so great, why doesn’t everyone use XLSB rather than XLSX?

So, if XLSB is so advantageous, why not everyone is using it as the default file format for saving workbooks? Well, there are some disadvantages to using XLSB files compared to the advantages it offers. And for these reasons, it is not the default file format for saving workbooks.

  • Lack of Interoperability – XLSB is a binary file format and it can’t be used in third party tools such as OpenOffice. Moreover, most of the 3rd party APIs won’t be able to work with XLSB files due to non-availability of internal details.
  • Compatibility – XLSB is not supported with earlier versions of Excel that were available prior to Excel 2007. For this reason, XLSB files can’t be opened in older versions of Excel.
  • Security – VBA files don’t give any indication about the presence of Macros in it unlike the XLSX and XLSM file formats. This can lead to security issues


XLSB files are smaller, efficient to open and save, and storage efficient as compared to popular XLSX and XLSM files. However, most modern Spreadsheet files opening applications work better with the open-specifications-based XLSX files rather than XLSB files. For this reason, XLSX remains the default file format of work in Excel.