How to convert a XLS to a XLSX file?

Zamzar Pro Tip: You can use Microsoft Office, Libre Office or if you own a Mac you can use Numbers to open XLS files.

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File extension	.xls
Category	Document File
Description	Microsoft Excel is a commercial spreadsheet application written and distributed by Microsoft for Microsoft Windows and Mac OS X. Pre-2007 versions of Excel use XLS as the primary format for saving files. It features calculation, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications. It has been a very widely applied spreadsheet for these platforms, especially since version 5 in 1993, and it has almost completely replaced Lotus 1-2-3 as the industry standard for spreadsheets. Excel forms part of Microsoft Office. The current versions are 2010 for Microsoft Windows and 2011 for Mac OS X.
Actions	XLS Converter View other document file formats
Technical Details	Microsoft Excel up until 2007 version used a proprietary binary file format called Binary Interchange File Format (BIFF) as its primary format. Used as the basis for XLS files it is a persistence format that supports authoring and manipulating content in workbooks and workbook templates. Most versions of Microsoft Excel can read CSV, DBF, SYLK, DIF, and other legacy formats.
Associated programs	Microsoft Excel Microsoft Excel Viewer OpenOffice
Developed by	Microsoft
MIME type	application/vnd.ms-excel
Useful links	More detail about the XLS format How to open an XLS file without Microsoft Excel Microsoft Office binary file format specifications

File extension	.xlsx
Category	Document File
Description	As part of Microsoft's 2007 Office suite of products another open XML document type was introduced. This time in the Excel sphere, Excel is known world wide. It is a powerful tool you can use to create and format spreadsheets, graphs, do complex maths and much more. You are able to create diverse spreadsheets with multiple workbooks, formulae, and various data sources. Files can be saved in the XLSX format, which is based on the Open XML format and uses ZIP compression for smaller file sizes.
Actions	XLSX Converter View other document file formats
Technical Details	XLSX improves file and data management and data recovery. XLSX extends what is possible with the binary files of earlier versions. Any application that supports XML can access and work with data in the new file format. The application does not need to be a Microsoft product it can be any application. Users can also use standard transformations to extract or repurpose the data. In addition, security concerns are drastically reduced because the information is stored in XML, which is essentially plain text. Thus, the data can pass through corporate firewalls without hindrance.
Associated programs	Microsoft Excel 2007 OxygenOffice Progessional (Linux) OpenOffice
Developed by	Microsoft
MIME type	application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Useful links	More detail about the XLSX format

Using Zamzar, it is possible to convert XLS files to a variety of other formats

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