XLS to XLSX

What it does

It takes a spreadsheet in Excel’s old binary format — the one that ends in .xls, which newer programs open with a warning or refuse outright — and writes an .xlsx instead. Values, sheets and sheet names come through.

It also reads the two files that only resemble an .xls by name, and those are the most common of all.

The format is read from the bytes, not the extension

A file called .xls is often something else entirely. “Export to Excel” across half the web produces an HTML table; Excel’s own “save as web page” does the same; some business systems write a CSV and give it the wrong extension. They open in Excel, which is what convinces people they are spreadsheets.

This tool looks at the first bytes and says what it found before converting. If you uploaded what you believed was an Excel file and you read “an HTML table with an .xls extension”, that line answers every question that would come after it.

The preview is cut short, and says so

You see the first rows of the chosen sheet, not all of them, with the real count beside it. Columns are counted on the longest row, not on the header, because a spreadsheet exported by a business system almost always has a short header and wider rows below it.

If the file holds several sheets you pick which one to look at. All of them go into the .xlsx regardless.

A file that opens is not a file that converted

The library that reads spreadsheets never refuses: faced with bytes it does not understand it falls back to delimited text and returns a table anyway, full of unreadable characters. A converter built on top of that behaviour produces a valid, meaningless .xlsx — the worst defect in this category, because it looks like it worked.

Here the format is decided first, and a file that opens without holding a single cell is rejected rather than converted.

What it does not do

Macros, charts, pivot tables and complex formatting do not come through. The data comes out, not the work built around the data. If the spreadsheet matters because of its macro, this is not the road: that needs Excel or LibreOffice.

Password-protected files do not open. There is no partial way to read them, and trying would produce a sheet of random characters. The protection has to be removed first, with the program that set it.

Large files are a memory problem. A spreadsheet is not read, it is expanded: every cell becomes an object, then has to be written back out as XML. Past a certain size a warning appears — not a refusal, because on a recent machine that file goes through.

About your data

Nothing leaves this page and nothing is saved.