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What is it
XLSX is Microsoft Excel's default spreadsheet format — an XML-based container that powers everything from household budgets to Fortune 500 financial models. Spreadsheets rule the world. This is their container. Like DOCX, it is actually a ZIP archive of XML files — you can rename one to .zip and peek inside if you are curious. XLSX supports formulas, charts, pivot tables, conditional formatting, and multiple sheets. The older .xls format was a binary blob limited to 65,536 rows; XLSX handles over a million. For raw data exchange, CSV is simpler. For anything involving calculations or presentation, XLSX is the standard.
Technical details
Safety
What opens it
Microsoft Excel
Google Sheets
LibreOffice Calc
Apple Numbers
FAQ
What is the difference between XLSX and CSV?
CSV is plain text — just commas and values. XLSX is a full spreadsheet with formulas, formatting, multiple sheets, charts, and data types. Use CSV when you need maximum compatibility or are feeding data to code. Use XLSX when humans need to read, filter, or calculate.
How do I open an XLSX file without Excel?
Google Sheets opens XLSX files directly in your browser. LibreOffice Calc (free, all platforms) and Apple Numbers also work. Complex formulas or macros may not translate perfectly, but for most files you will not notice a difference.
What is the difference between XLSX and XLS?
XLS is the legacy binary format from Excel 97–2003, limited to 65,536 rows and 256 columns. XLSX uses open XML, supports over 1 million rows and 16,384 columns, produces smaller files, and works with more software. There is no reason to save as XLS unless someone specifically asks.
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