XLS converter Add documents Click here to choose files or Drop them hereUp to 50 files#Source fileSizeStatus Input format:XLSX, CSV, ODS Automatically start I consent to collecting, storing and processing my data from this form according to Privacy Policy and Terms of Use.ConvertXLS – Microsoft Excel Binary File FormatFormat introductionMicrosoft Excel up until 2007 version used a proprietary binary file format called Excel Binary File Format (.XLS) as its primary format. Excel 2007 uses Office Open XML as its primary file format, an XML-based format that followed after a previous XML-based format called “XML Spreadsheet”.Technical detailsOpenOffice.org has created documentation of the Excel format. Since then Microsoft made the Excel binary format specification available to freely download.