XLS (Excel 97–2003 Workbook) and XLSX (Microsoft Excel Workbook) are built for different jobs. XLS is typically used for legacy spreadsheets, while XLSX is best for spreadsheets, reports. Converting lets you open, share or upload your files wherever XLSX is expected.
How to use the XLS to XLSX converter
- Add your XLS filesClick “Choose Files” or drag and drop them into the box. You can add many files at once — or paste a file with Ctrl+V.
- Choose XLSX and adjust settingsXLSX is selected automatically. Optionally open Settings to change output options.
- Convert and downloadPress “Convert”. Your XLSX files appear instantly — download them one by one or all together as a ZIP.
XLS vs XLSX
XLS Excel 97–2003 Workbook
XLS is the older binary Excel format, still produced by legacy systems and banks.
- Compression
- Binary
- Features
- Legacy Excel
- Origin
- 1997, Microsoft
- Best for
- Legacy spreadsheets
XLSX Microsoft Excel Workbook
XLSX is the standard Excel spreadsheet format with multiple sheets, formulas and formatting. Google Sheets, Numbers and LibreOffice open it too.
- Compression
- ZIP-compressed XML
- Features
- Multiple sheets, formulas
- Origin
- 2007, Microsoft
- Best for
- Spreadsheets, reports
Why use ConvertMathly?
Files are processed on your device and never uploaded. Close the tab and they are gone.
No account, no daily cap, no queue and no watermark — convert as much as you want.
No waiting for uploads or downloads: results are ready as fast as your device can process them.
Windows, Mac, Linux, Chromebook, iPhone and Android — any modern browser, nothing to install.
Frequently asked questions
How do I convert XLS to XLSX?
Add your XLS files above, make sure XLSX is selected and press Convert. The XLSX files are ready to download a few seconds later — no installation or account required.
Is there a file size or daily limit?
No. Since everything runs locally, there are no daily caps, queues or file size limits beyond what your device can handle.
Are my XLS files uploaded to a server?
No. ConvertMathly converts files entirely inside your web browser using JavaScript and WebAssembly. Your files never leave your computer or phone, which makes it safe for private photos and documents.
Can I convert multiple XLS files at once?
Yes — add as many files as you like. They are converted one after another and you can download everything in a single ZIP.