Upload the .xls here — the converter rewrites it as .xlsx without Excel ever opening the workbook, which also means no macro code executes during conversion. For whole folders, the desktop Total Excel Converter does the same from the command line.

Depending on your needs, XLSX may be better for you than XLS. While XLS is usable in any version of Microsoft Excel, supports Macros, and works faster than XLSX, it does have limits to the amount of data it can store, and is less robust than the XLSX format. XLSX is widely compatible with non-Microsoft-based devices, but can only be opened on versions of Excel 2007 or later. It doesn’t support Macros, but it can save more data in smaller file sizes than XLS. If you need to convert your XLSX file to XLS format, you can easily do that with the free conversion tool on Zamzar’s website.

XLS is an earlier version of XLSX, and XLS files can be opened in all versions of Office and can support macros. However, XLSX has been the standard Microsoft format since 2007, is more robust and tends to have a smaller file size – so if you don’t need support for macros then it may be the better choice.

It’s easy to convert between both formats by using an online conversion tool like Zamzar. Just upload one or more Excel spreadsheets, select to convert to either XLSX or XLS, and then download your new copy of the file.