Convert XLS to XLSX Online Free — No Upload, Formatting Kept
Upgrade legacy .xls workbooks (Excel 97–2003) to modern .xlsx right in your browser — formulas and formatting stay intact. No upload, no signup, no limits.
Drop .xls files here, or click to browse
Supports .xls (Excel 97–2003) · processed locally · never uploaded
How to Convert XLS to XLSX Online
- Drop one or more .xls files into the box above — files are processed locally and never uploaded.
- Click Convert to XLSX — every workbook is parsed and repacked in the modern OOXML format.
- Check the report — each file lists the worksheets that were converted, by name.
- Download — a single file downloads directly; multiple files come back bundled as a ZIP.
How It Works
A .xls file is a binary BIFF stream inside an OLE compound document. This tool reads that stream directly in your browser, rebuilds the workbook as an in-memory model — cells, formulas, styles, sheet order — then serializes that model as a fresh OOXML package: one XML part per worksheet, plus shared-string, style and metadata parts, all zipped into a .xlsx blob. The entire round-trip runs locally; no byte ever touches a server.
Your file never leaves your device. Both parsing and repackaging happen in JavaScript inside the browser — no upload, no queue, and no file-size limit beyond what your machine can hold in memory.
Compared to Excel "Save As"
The usual routes from .xls to .xlsx are opening the file in Excel and picking "Save As", or pasting it into a free online converter. This tool sits between the two — local like Excel, free like the web converters.
| Approach | Where your file goes | What to expect |
|---|---|---|
| This tool | Nowhere — stays in your browser | Free · no signup · no size cap · batch via ZIP |
| Excel "Save As" | Stays on your PC | Needs Excel installed; one file at a time |
| Free online converters | Uploaded to a server | Free tiers cap size; files leave your device |
Why Switch from XLS to XLSX
The .xls format dates back to Excel 97 and stores a workbook as a maze of binary records inside an OLE compound file. Modern .xlsx instead packages XML files in a ZIP archive, which makes files smaller, far more resistant to corruption, and readable by virtually every current tool — cloud editors, scripts, and the other utilities on this site.
Excel has saved in .xlsx by default since 2007, and many services now refuse .xls outright. Converting once, properly, ends the compatibility struggle: the converted file behaves exactly like any workbook saved by current Excel.
A workbook that demands a password before opening is encrypted at file level. Encrypted .xls files cannot be converted without that password — no honest tool can read them.
XLS vs XLSX at a Glance
Both formats carry the same core ideas — sheets, cells, formulas — but under the hood they could not be more different.
| Aspect | .xls (Excel 97–2003) | .xlsx (Excel 2007+) |
|---|---|---|
| Internal structure | Binary records in an OLE compound file | XML files in a ZIP archive |
| Maximum rows per sheet | 65,536 | 1,048,576 |
| Maximum columns per sheet | 256 | 16,384 |
| File size | Larger for the same data | Typically 25–75% smaller |
| Corruption resistance | One bad record can break the whole file | Parts are independent and often recoverable |
| Support status | Legacy — kept for compatibility only | Current default of Excel, Sheets and LibreOffice |
What the Conversion Preserves
The converter reads the BIFF records of the source file and rebuilds them as OOXML, keeping the workbook structure intact.
- Cell values — text, numbers, booleans and error codes stay exactly as they were.
- Dates keep their underlying serial number and display format, so they look identical in Excel.
- Formulas are carried over with their cached results and recalculate when the file opens.
- Multiple sheets keep their names and order, along with basics like column widths and merged cells.
Limitations
- Only .xls (Excel 97–2003, BIFF8) is accepted — .xlsx, .xlsm and .ods are already convertible with the other tools on this site.
- VBA macros in .xls files are dropped, because .xlsx cannot store macros. Save macro workbooks as .xlsm in Excel instead.
- Embedded legacy objects such as OLE charts may be simplified to static pictures or omitted.
- Only convert files you own or have permission to modify.
Frequently Asked Questions
Is this XLS to XLSX converter really free?
Yes — 100% free, with no sign-up, no watermark and no file limit. Everything runs in your browser.
Are my files uploaded to a server?
No. Parsing and repacking happen entirely in your browser with JavaScript; your file never leaves your device.
Will formulas and dates survive the conversion?
Yes. Formulas are transferred with their last calculated result and recalculate on open; dates keep their serial value and display format.
Why should I bother converting old .xls files?
XLSX files are smaller, allow over a million rows per sheet, resist corruption better, and are accepted by modern tools that increasingly reject .xls.
Can it convert a password-protected .xls file?
If a password is required to open the file, no — that is genuine encryption. Mere sheet protection without an open password does not block conversion.
What happens to macros in my .xls workbook?
They are removed, because .xlsx cannot store VBA macros. Keep the original .xls or save as .xlsm if you still need the code.
Can I convert several files at once?
Yes. Drop multiple .xls files and convert them in one pass; the results download together as a ZIP.
The converted file looks slightly different — why?
Most workbooks convert pixel-perfect. Exotic legacy features (old chart types, OLE objects, custom toolbars) have no modern equivalent and may be simplified or dropped.
Related Tools
Need to view or edit the converted workbook afterwards?
Open the free online Excel editor