Since the launch of Microsoft Office 2007, Microsoft changed the default file extension for Microsoft Excel files to .xlsx. This new file format is part of Microsoft's Open XML format, which results in a smaller file size and better data integration with external sources. If you have a file with the extension .xls, you can easily convert it to the newer .xlsx file format.
- Open the file that you want to convert in Microsoft Excel.
- Click the round "Office" button in the top left corner of the screen to open the file menu.
- Click "Save As."
- Select "Excel Workbook" from the menu. Select the location where you want to save your file, give it a name and click "Save." Your file will now be saved with the file extension .xlsx instead of .xls.