Convert XLS files to XLSX free in your browser — no signup, no install, and the file is never uploaded to a server. XLSX keeps full quality with no further loss.
Add your XLS file
Drag the XLS file onto the drop area above, or click it to pick a file from your device. You can add several files at once.
Confirm XLSX as the output
XLSX is already selected as the output format on this page. Only the options this format actually supports show up, such as a page range or sheet selection.
Run the conversion
Press the convert button. Processing happens on your own device, so the time depends on your computer rather than a server queue.
Download the XLSX file
When it finishes, download the XLSX file. Converting multiple files gives you the option to download them together as a ZIP.
Excel's older binary format, limited to 65,536 rows per sheet. Modern Excel still opens it, but newer features cannot be saved.
Microsoft Excel's standard format, preserving formulas, charts, multiple sheets, and formatting. Internally it is a zip archive of XML.
Yes. XLS to XLSX conversion is completely free with no signup, no watermark, and no daily limit on the free plan for ordinary use.
No. The conversion runs entirely inside your browser using WebAssembly, so the XLS file never leaves your device. That is also why it works without an internet connection once the page has loaded.
It can go either way. Both formats are lossless, so nothing is thrown away — the size difference comes from how each one packs the same data.
The free plan handles files up to 200MB. Because processing happens on your own device, very large files depend on your computer's memory rather than a server quota.
Spreadsheet converter
What each file format is, what it is used for, and which formats it can be converted to.
Open converter Browse the full format reference