For workbooks in Excel 2003, the extension .xls is used.
The file extension of MS Excel is .xmls
XLS is the main extension name used in Excel.
The standard extension for Excel workbooks is xls for versions up to 2003. Excel 2007 uses xlsx as its extension for workbooks.
.xls or .xlsx
xls, xlsx (2007)
.xls for versions up to Excel 2003 and .xlsx from Excel 2007 onwards.
The extension for excel is .xls
.ppt is the extension of PowerPoint. .xls is the extension of Excel.
The three letter extension of Excel is XLS.
.xl is the file extension for Excel documents.