Excel File Extensions and Their Uses

Excel File Extensions: XLSX, XLSM, XLS, XLTX and XLTM

Common Excel File Extensions and Their Uses
Common Excel File Extensions and Their Uses. © Ted French


A file extension is the group of letters that appear after the last period in a file name for computers running the Windows operating system. File extensions are usually 2 to 4 characters long.

File extensions are related to the file format, which is a computer programming term that specifies how information is coded for storage in a computer file.

In the case of Excel, the current default file extension is XLSX and has been since Excel 2007.

Prior to that, the default file extension was XLS.

The difference between the two - besides the addition of the second X - is that  XLSX is a XML-based open file format, while XLS is a proprietary Microsoft format.

XML Advantages

XML stands for extensible markup language and it is related to HTML (hypertext markup language) the extension used for web pages.

According to the Microsoft web site, the advantages of the newer file format  include:

  • smaller file sizes for storage and transfer;
  • better recovery of information from damaged files;
  • easier detection of files containing macros.

This last advantage stems from the fact that excel files containing VBA and XLM macros use the XLSM extension rather than XLSX. Since macros can contain malicious code that can damage files and compromise computer security, it is important to know if a file contains macros before it is opened.

The newer versions of Excel can still save and open XLS files for the sake of compatibility with earlier versions of the program.

Changing File Formats with Save As

Changing file formats can be accomplished through the Save As dialog box, as shown in the image above. The steps for doing so are:

  1. Open the workbook that is to be saved with a different file format;
  2. Click on the File tab of the ribbon to open the drop down menu;
  3. Click on Save As in the menu to open the Save As panel of options;
  1. Choose a location or click on the Browse button to open the Save As dialog box;
  2. In the dialog box , accept the suggested file name or type a new name for the workbook;
  3. In the Save as type list, choose a file format for saving the file;
  4. Click Save to save the file in the new format and return to the current worksheet.

Note: if you are saving the file in a format that does not support all the features of the current format - such as formatting or formulas - an alert message box will appear informing you of this fact and giving you the option of cancelling the save. Doing so will return you to the Save As dialog box.

Opening and Identifying Files

For most Windows users, the main use and benefit of the file extension is that it allows them to double click on a XLSX, or XLS  file and the operating system will open it in Excel.

In addition, if file extensions are viewable, knowing which extensions are associated with which programs can make it easier to identify files in My Documents or Windows Explorer.

XLTX and XLTM File Formats

When an excel file is saved with either an XLTX  or XLTM extension it is saved as a template file. Template files are intended to be used as starter files for new workbooks and they normally contain saved settings such as the default number of sheets per workbook, formatting, formulas, graphics, and custom toolbars.

The difference between the two extensions is that the XLTM format can store VBA and XML (Excel 4.0 macros) macro code.

The default storage location for user-created templates is:

C:\ Users\ [UserName] \ Documents\ Custom Office Templates

Once a custom template is created, it and all subsequently created templates will automatically be added to the Personal list of templates located under File > New in the menus.

Excel for Macintosh

While Macintosh computers do not rely on file extensions for determining which program to use when opening a file, for the sake of compatibility with Windows versions of Excel, newer versions Excel for the Mac - as of version 2008, use the XLSX file extension by default.

For the most part, Excel files created in either operating system can be opened by the other. One exception to this is Excel 2008 for the Mac which did not support VBA macros.

As a result, it cannot open XLMX or XMLT files created by Windows or later Mac versions of the program that do support VBA macros.