What is a .xlsx file?
Microsoft Excel Open XML Spreadsheet · Document · Microsoft · 2007
XLSX is the modern Excel spreadsheet format. Like DOCX it is a zipped bundle of XML, holding your cells, formulas, charts and multiple sheets, and it opens in Excel, Google Sheets and LibreOffice alike.
What is a .xlsx file used for?
XLSX stores everything a spreadsheet needs: values, formulas, formatting, charts, pivot tables and many sheets, all as compressed XML.
It replaced the old binary XLS in 2007 and is now the universal spreadsheet format across office suites.
For raw data without formatting or formulas, the simpler CSV format is often exchanged instead.
What opens a .xlsx file?
The .xlsx format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Excel
- LibreOffice Calc
- Google Sheets
macOS
- Excel
- Numbers
- LibreOffice Calc
Linux
- LibreOffice Calc
- OnlyOffice
- Google Sheets
Web
- Google Sheets
- Office on the web
Open a .xlsx file step by step
- Confirm the file really is a .xlsx. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Excel or LibreOffice Calc.
- On Mac, use Excel or Numbers.
- On Linux, try LibreOffice Calc or OnlyOffice.
- Still stuck? Convert the .xlsx to CSV, which opens more widely.
Why can't I open my .xlsx file?
Almost always because no installed app understands XLSX. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .xlsx at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .xlsx file
You can convert a .xlsx file to CSV, PDF, ODS.
LibreOffice Calc converts XLSX to CSV and ODS. A CSV export keeps one sheet and the values only: formulas, formatting, charts and every other sheet are gone.
What is the .xlsx file signature (magic bytes)?
A .xlsx file starts with the hex bytes 50 4B 03 04, which read as PK.. in ASCII. Programs identify XLSX by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for XLSX. For a full breakdown, see the ZIP file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 50 4B 03 04 | 0 | PK.. | ZIP header (Office Open XML) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .xlsx file?
XLSX is the modern Excel spreadsheet format. Like DOCX it is a zipped bundle of XML, holding your cells, formulas, charts and multiple sheets, and it opens in Excel, Google Sheets and LibreOffice alike.
How do I open an XLSX for free?
Use Google Sheets, LibreOffice Calc or the free web version of Excel. All open XLSX with formulas intact.
Should I use XLSX or CSV?
Use XLSX when you need formulas, formatting or multiple sheets. Use CSV for plain, portable data that any program can import.