How do I convert XLS to XLSX?

Add your XLS file to the upload area above, then press Convert. The XLSX file downloads straight to your device. You do not need an account, and there is no watermark.

Are my files uploaded to a server?

No. This conversion runs entirely inside your browser using WebAssembly, so the file never leaves your device — you can even disconnect from the internet after the page loads and it will still work.

Does converting to XLSX reduce quality?

Text, structure and images carry over faithfully. Exact page layout does not, because XLSX lays content out differently from XLS. Check headings, tables and page breaks in the result.

How large a file can I convert?

Up to 100 MB per file for this conversion. Because the work happens in your browser, the practical limit is your device's memory — larger files work on a desktop with plenty of RAM and may fail on an older phone.

Can I convert several files at once?

Yes. Add as many as you like and press Convert All. Each file is processed independently, so one failure does not stop the rest, and you can download everything together as a ZIP.

Can I use this on my phone?

Yes. FileTools360 works in mobile browsers on iOS and Android, including choosing files straight from your camera roll. Very large videos may run out of memory on a phone — those are better converted on a laptop.

SpreadsheetLayout rebuiltRuns in your browser

XLS to XLSX Converter

Turn XLS files into XLSX in a couple of clicks. Excel's pre-2007 binary workbook. The modern Microsoft Excel workbook format. Content is preserved and the layout is rebuilt for the target format.

On your deviceNever uploadedGone when you close the tabHow this works

Drop your files here

XLS files (.xls) · up to 100 MB each

or paste files from your clipboard

Ready when you are

Drop a XLS file above and FileTools360 will turn it into XLSX — right here on your device, without uploading anything.

⌘K to search converters

How to use it

1
Add your XLS files
Drag them onto the upload area, choose them from your device, or paste them from your clipboard. You can queue several at once.
2
Adjust the settings if you want to
The defaults suit most people. Open Advanced to control delimiter and header handling.
3
Convert and download
Press Convert. Everything happens on your own device — nothing is uploaded. Download files one by one, or grab them all as a ZIP.

XLS and XLSX explained

The pre-2007 Excel format is a binary structure limited to 65,536 rows and 256 columns — limits modern datasets routinely exceed.

XLSX is Excel's modern format — a ZIP of XML holding cells, formulas, formatting, multiple sheets, charts and pivot tables.

Where XLS files come from: Spreadsheets from Excel 2003 or earlier, and some legacy export systems.
Where XLSX is used: Excel, Google Sheets exports and business reporting systems.

XLS vs XLSX

The two formats solve different problems, which is why converting between them involves trade-offs rather than a straight upgrade.

XLS compared with XLSX
Property	Source	Target
Compression	None	Lossless
Introduced	1987	2007
Browser support	Still opens in Excel and LibreOffice.	Excel, Google Sheets, Numbers, LibreOffice.

XLS is stronger at: Still opens in Excel and LibreOffice.
XLSX is stronger at: Formulas, formatting, charts and multiple sheets in one file. Compact relative to the old .xls. Supported by Excel, Sheets, Numbers and LibreOffice.

Why convert XLS to XLSX?

People make this switch when they run into the limits of XLS: anything else — XLSX is better in every respect. XLSX is the better fit when the data needs calculation, formatting or more than one sheet.

XLS limitations that prompt the switch: Hard row and column limits. Larger files than XLSX. Binary format that is awkward to parse.
What you give up: Harder to parse programmatically than CSV. Formula compatibility varies between applications.

What is preserved when converting XLS to XLSX?

Both formats store the content without discarding data, so this conversion preserves it exactly. The file size may change because the two formats compress differently, but the content itself is unaffected.

About these formats

Source

Legacy Excel Workbook

Excel's pre-2007 binary workbook.

Extensions: .xls
MIME type: application/vnd.ms-excel
Best for: Legacy systems that reject XLSX
Compatibility: Still opens in Excel and LibreOffice.

Target

Excel Open XML Workbook

The modern Microsoft Excel workbook format.

Extensions: .xlsx, .xlsm
MIME type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Best for: Multi-sheet data · Formulas · Business reporting
Compatibility: Excel, Google Sheets, Numbers, LibreOffice.

Good to know