XLS to XLSX Converter
Upgrade an old Excel 97-2003 (XLS) workbook to the modern XLSX format.
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About Converting XLS to XLSX
XLS is the old binary Excel format from Excel 97-2003, capped at 65,536 rows and prone to corruption. XLSX, introduced in Excel 2007, is an open XML-based ZIP package that supports over a million rows, compresses much smaller, and is the format every modern spreadsheet tool prefers. Converting XLS to XLSX modernises your workbook while keeping it fully editable.
PrivConvert upgrades the workbook through the LibreOffice engine, preserving every sheet, formula, cell format and chart. The conversion runs entirely in memory and your original file is erased the moment the XLSX is ready.
Common use cases
- Lifting the old 65,536-row limit so you can work with much larger datasets
- Modernising legacy workbooks so they open without compatibility warnings in current Excel
- Reducing file size — XLSX is compressed and typically far smaller than XLS
- Preparing a workbook for Google Sheets or Microsoft 365, which favour XLSX
- Fixing fragile or occasionally corrupting binary XLS files
Tips for best results
- All worksheets, not just the first, are preserved — XLSX keeps the full workbook intact.
- Formulas, named ranges and most charts carry over; very old XLM macros are not supported in XLSX.
- Conditional formatting and cell styles are retained during the upgrade.
- If the workbook contains VBA macros, save it as .xlsm instead to keep them — plain .xlsx strips macros by design.
How to Convert XLS to XLSX Online
You can convert XLS to XLSX right in your browser in under a minute. What you gain with XLSX: formulas, charts and multiple sheets.
Drag and drop your file into the upload area, click to browse your device, or paste a URL to a file hosted online. You can upload files up to 250 MB and batch convert up to 20 files at once.
Once uploaded, the conversion from XLS to XLSX starts automatically. The process runs entirely in an isolated environment - your data never leaves the secure pipeline.
Your converted file is ready instantly. Click the download button to save it to your device. The file is deleted from memory immediately after download.
Why choose PrivConvert?
Converting XLS to XLSX should not mean handing a stranger a permanent copy of your data. PrivConvert processes everything in memory and forgets it instantly.
Files are processed in volatile memory (RAM) and purged the instant your download is ready — nothing is ever written to disk, cached or backed up.
Every upload and download is protected with TLS 1.3, so your document cannot be intercepted on the way to the server or back to you.
Convert instantly with no sign-up, no email and no profiling cookies. We never build a profile around you or the files you convert.
Runs in any modern browser on Windows, macOS, Linux, Android and iOS — no install, plugin or desktop software needed.
XLS vs XLSX - Format Comparison
| Feature | XLS | XLSX |
|---|---|---|
| File extension | .xls | .xlsx |
| Supported by PrivConvert | Yes (as input) | Yes (as output) |
| Privacy-safe conversion | In-memory, zero storage | |
| Max file size | 250 MB per file | |
| Batch support | Up to 20 files simultaneously | |
A converter you do not have to worry about
PrivConvert handles thousands of conversions every day for developers, designers and privacy-conscious people who need a document converted without handing over a permanent copy.