FileopiaXLS to XLSX
XLS to XLSX Fast, secure, browser-local processing with zero file limits.
- Upload
- Options
- Download
- ✓ 100% free
- ✓ No sign-up
- 🔒 Files never leave your device
How to: XLS to XLSX
- Upload your older .xls workbook.
- Our parser reads binary records and rebuilds modern OpenXML.
- Download your modern, universal .xlsx file.
Why use Fileopia for XLS to XLSX?
| Fileopia | Typical upload-based sites | |
|---|---|---|
| Files uploaded to a server | No – processed on your device | Yes |
| Sign-up required | Never | Often for bigger jobs |
| Hourly / daily task limits | None | Common on free plans |
| Watermark on output | Never | Sometimes |
| Works offline after loading | Yes, for most tools | No |
Your files never leave your device
XLS to XLSX runs entirely in your browser using JavaScript and WebAssembly. Your files are read from your disk into this tab, processed in memory and saved straight back to your downloads folder – they are never uploaded to Fileopia or any third party.
- Test it yourself: once this page has loaded, switch off Wi‑Fi or mobile data and run the tool – it keeps working.
- Check the network: open your browser’s developer tools (F12 → Network) while processing; you will see no file upload requests.
- Nothing to delete: close the tab and the data is gone – there is no server copy, no retention period and no account.
File tools designed for local processing work in your browser. Practical file-size and performance limits depend on the selected tool, browser and device. Some features need an internet connection to load code or data.
Frequently asked questions
Why upgrade XLS to XLSX?
XLS is limited to 65,536 rows and lacks modern Excel features, while XLSX supports over 1,000,000 rows and is universally supported.
Is XLS to XLSX really free?
Yes. Every tool on Fileopia is free to use with no account required and no watermarks; practical file limits vary by tool and device. The site is supported by unobtrusive ads.
Are my files uploaded to a server?
No. Fileopia processes your files directly in your browser using JavaScript. Your documents never leave your device, so they stay completely private.
Does it work on mobile?
Yes. Fileopia works in any modern browser on Android, iPhone, iPad, Windows, Mac and Linux.