XLS to XLSX

Anyone who has opened a decade-old accounting export from a retired inventory system knows the drill: modern office apps increasingly balk at .xls (Excel 97-2003) - some cloud tools refuse the import outright, others just flash a warning about the outdated format. This tool converts the aging .xls workbook straight in your browser into a modern .xlsx file, so it opens cleanly in Excel, LibreOffice, Google Sheets and any other current app.

The conversion carries over the entire numeric payload: entered values, the last results formulas calculated, number formats like currency or percentage displays, and merged header cells all survive. Everything runs entirely in the browser through a lean JavaScript library that reads the binary BIFF format - no install, no waiting on a server.

An honesty note: fonts, cell colours and border lines are lost in this conversion, because the library used cannot write formatting back out when saving .xlsx - only the plain number and text content comes through cleanly. Anyone who needs the visual design has to rebuild it in the destination program.

Specifications

In 3 steps

1. Drop or pick your legacy Excel file (.xls).
2. The tool converts it to XLSX locally.
3. Download the .xlsx file.

Limitations: Numeric values, calculated formula results, number formats and merged cells arrive unchanged in the new workbook. Visual design (font, fill colour, border line) cannot technically be written back out when saving .xlsx. Conditional formatting, data validation and embedded charts from the .xls file are not carried over either; a sheet holding an embedded chart arrives as an empty sheet. Encrypted, password-protected .xls files are rejected with a clear error message.

FAQ

Related tools

XLS to CSV · ODS to XLSX · ODS to CSV · CSV to XLSX · XLSX to CSV · Split XLSX