What is the difference between XLS and XLSX?

XLS is the pre-2007 Excel binary workbook format. It is still emitted by legacy systems and older export routines, and remains readable by current spreadsheet software, though support is being phased out in favour of XLSX. XLSX is the standard Excel workbook format: a ZIP archive of XML files describing sheets, cells, formulas and formatting. It has been the Excel default since 2007 and is readable by Google Sheets, LibreOffice and Numbers.

Will I lose anything converting XLS to XLSX?

No. Both formats represent the same data model, so the values and their structure come across intact. Converting XLSX to CSV keeps one sheet only, and exports the computed values rather than the formulas that produced them.

Anything to watch out for with XLSX?

Converting XLSX to CSV keeps one sheet only, and exports the computed values rather than the formulas that produced them. Cell formatting, colours, merged cells and charts have no CSV equivalent and are dropped.

What happens to formulas?

Formulas are carried across between workbook formats.

What if my workbook has multiple sheets?

All sheets are preserved — both formats are multi-sheet containers.

What should I know about starting from XLS?

XLS is the pre-2007 binary format, capped at 65,536 rows and 256 columns per sheet, and increasingly deprecated by the software that reads it. More broadly: XLS is the legacy Excel binary format, the default until Office 2007. It is still produced by older enterprise systems and by export routines nobody has revisited in fifteen years.

When is XLSX the right choice?

XLSX suits: workbooks with multiple sheets or formulas; anything a colleague will open in Excel; preserving cell formatting and number formats. It is the wrong choice when programmatic ingestion, where CSV or JSON is simpler to parse.

Is there a file size limit?

No hard limit — the constraint is your browser's memory. Files under 50MB convert in a few seconds. Larger files work but take longer, and a browser tab typically has 250-500MB to play with, so very large batches are better split into smaller groups.

Does this work on mobile?

Yes. The drop zone falls back to your phone's file picker, and the conversion runs on-device exactly as it does on desktop. Large files are slower on a phone because there is less CPU and memory available, but nothing about the workflow changes.

Convert XLS to XLSX

Convert legacy XLS workbooks to XLSX, lifting the old 65,536-row ceiling. Free, in your browser, no upload.

Drop spreadsheet files to convert

XLSX, XLS, ODS, CSV

Files stay on your device. Open DevTools' Network tab to verify.

Overview

Why convert XLS to XLSX

XLSX is the more practical choice here. Workbooks with multiple sheets or formulas

Comparison

XLS vs XLSX: what actually differs

XLS compared with XLSX across encoding, fidelity, file size and support.
Attribute	XLS	XLSX
Full name	Excel Binary Interchange Format	Office Open XML Workbook
Encoding	Binary	Binary
What it preserves	Multiple sheets and formulas, with older limits	Full — multiple sheets, formulas, formatting, charts
Typical size	Larger than XLSX for the same content — no ZIP container	Compact for what it carries; the container is ZIP-compressed
Support	Read by Excel, LibreOffice and Google Sheets; increasingly deprecated.	Excel, Google Sheets, LibreOffice, Numbers, and most BI tools.

How to

How to convert XLS to XLSX

01
Drop your XLS file
Drag one or more XLS files onto the drop zone above, or click to browse. Files stay on your device — there is no upload step.
02
Convert to XLSX
convert.now parses the XLS and writes it out as XLSX in a Web Worker, so the page stays responsive even on large files. Nothing is sent anywhere.
03
Download the result
Download the XLSX file, or a zip of all of them for a batch. Filenames are preserved, with the extension changed to .xlsx.

Why here

Why convert.now

Private
Files stay in your browser. No upload step. Nothing for anyone to see.
Fast
No queue, no upload wait. Conversion starts the moment you drop a file.
Free
No ads. No file-count limit. No sign-up wall. Just the converter.

FAQ

XLS to XLSX: common questions

No. The XLS to XLSX conversion runs entirely in your browser. Files never leave your device, and there is no server involved in the conversion at all. Open DevTools' Network tab and run a conversion if you want to confirm it — you will see the page and its code load, and no request carrying your file.

Related XLS converters

Last updated 27 August 2026

Why convert XLS to XLSX

XLS vs XLSX: what actually differs

How to convert XLS to XLSX

Drop your XLS file

Convert to XLSX

Download the result

Why convert.now

XLS to XLSX: common questions

Related XLS converters