XLS to XLSX Converter

AUTO-DELETE/Files are processed on our server and deleted as soon as conversion finishes.

or drop your images here

How to Convert XLS to XLSX Online

XLS to XLSX: what changes in the file

This tool takes a XLS file, converts it with LibreOffice running on our servers and returns a XLSX file.

XLS is the old binary Office 97–2003 format and XLSX the current XML format: the file gets smaller, opens in current Office and nothing is lost.

How XLS and XLSX differ

Property	XLS	XLSX
Full name	Excel 97–2003 Workbook (binary)	Office Open XML Workbook
Introduced	Microsoft, 1997	Microsoft, 2007 (ISO/IEC 29500)
Data type	laid-out document	laid-out document
Strengths	opens in every version of Excel	current Excel format; 1,048,576 rows × 16,384 columns per sheet
Limitations	limit of 65,536 rows × 256 columns per sheet	Excel 2003 and older need a compatibility pack

Measured with a sample file

On September 25, 2026 we ran the tool on our production server with a sample file: a 13-row spreadsheet with a formula (XLS), 6 KB.

Result: 6 KB → 5 KB, processed in 3.3 s. Output: a valid XLSX file (file signature checked).

Real sizes depend on document length, embedded images and fonts; the figures only show the order of change.

Before you convert

The server has DejaVu and Liberation fonts only. Times New Roman, Arial and Courier New keep their layout (Liberation matches their metrics); other fonts such as Calibri or Cambria are substituted, so line breaks and page count can change.
Up to 100 MB per file; a conversion that runs longer than 2 minutes is cancelled.
The file is sent to our server for conversion and deleted as soon as processing ends, including when it fails.

Frequently asked questions

Is any content lost converting XLS to XLSX?

No. XLSX can hold everything XLS contains, and the file is usually smaller thanks to ZIP compression.

Why did the page count or line breaks change?

The document uses a font the server does not have (only DejaVu and Liberation are installed), so a similar font is substituted. Times New Roman, Arial and Courier New are not affected.

How does the file size change from XLS to XLSX?

With our sample file: 6 KB → 5 KB. Your file may differ depending on its content.