Files and data
What is XLSX?
Short for Excel Open XML Spreadsheet. Also called Excel workbook.
XLSX is the standard Excel workbook format, storing sheets, formulas, formatting and data types in a compressed package of XML files.
How it works
Since Excel 2007, workbooks are saved as XLSX: a ZIP archive holding separate XML files for each worksheet, the shared list of text values, styles, charts and settings. That structure makes files compact and lets other programs read them without Excel.
Unlike CSV, XLSX keeps data types. A cell can be a number, a date, text or a formula, with its display format stored separately. It also supports multiple sheets, charts, comments, data validation and frozen headers.
XLSX vs CSV
XLSX is the better working format for people; CSV is the better exchange format for systems. Importing into a database or online tool usually wants CSV. Sharing a report with colleagues usually wants XLSX, so its sheets and formatting survive.
A practical example
A monthly report with a summary sheet, a data sheet and currency formatting saved as XLSX keeps all three. Saved as CSV, only the active sheet’s values survive.
What to watch out for
Formulas, merged cells and hidden sheets can hold data you didn’t mean to share. Check every sheet, or export a plain CSV of just the values before sending.
Tools you can use
- Excel to CSV · Every sheet, including old .xls files
- CSV to Excel · Keeps leading zeros and long IDs intact
Go a little deeper
- CSV vs Excel: what is the difference?
- How to open an .xls or .xlsx file without Excel
- Why Excel removes leading zeros from your data
Common questions
What is the difference between XLS and XLSX?
XLS is the older binary Excel format used before 2007. XLSX replaced it with a compressed XML format that is smaller, more robust and easier for other software to read.
Can I open an XLSX file without Excel?
Yes. Google Sheets, LibreOffice Calc and Apple Numbers all open XLSX files, and converting to CSV makes the data readable in almost anything.
Why is XLSX identified as a ZIP file?
An XLSX file is a ZIP archive containing XML files for each sheet, the styles and shared text. File type checkers have to look inside to tell it apart from a normal ZIP.