Glossary
What Is an XLSX File?
An XLSX file is an Excel workbook. It is the default format of Microsoft Excel since Excel 2007, and it stores worksheets with their values, formulas, number formats, colors, charts, and images. The format is Office Open XML SpreadsheetML, standardized as ECMA-376 and later as ISO/IEC 29500.
TL;DRAn XLSX file is a ZIP package of XML that stores an Excel workbook. Open it in Excel, LibreOffice, or Google Sheets, and compare or merge versions with a dedicated tool.
What Is Inside an XLSX File
An XLSX file is a ZIP package. Rename a copy to .zip and any archive tool opens it. Inside are plain XML files and a few resources:
- workbook.xml: the list of sheets and workbook settings.
- sheet1.xml, sheet2.xml, and so on: one file per worksheet, with the cells, values, and formulas.
- sharedStrings.xml: every text string, stored once and referenced by index from the sheets.
- styles.xml: fonts, fills, borders, and number formats.
- A media folder for pictures, and separate parts for charts.
The ZIP container is why XLSX files are smaller than the old XLS and why a damaged file can often be partly recovered: the XML for each sheet is a separate part.
XLSX vs XLS
XLS is the older binary format (BIFF) used up to Excel 2003. XLSX replaced it in Excel 2007. The worksheet size grew with it: XLS holds 65,536 rows and 256 columns per sheet, while XLSX holds 1,048,576 rows and 16,384 columns. XLSX also cannot carry macros, which is a deliberate safety choice.
XLSX vs XLSM, XLSB, ODS, and CSV
- XLSM: the same package as XLSX, but it can contain VBA macros. Excel refuses to store macros in a plain .xlsx.
- XLSB: a binary workbook. It opens faster on very large files but is harder for other programs to read.
- ODS: the OpenDocument spreadsheet used by LibreOffice. Excel reads and writes it, though some formatting may shift.
- CSV: plain text with values separated by commas. It has no formulas, no formatting, and only one sheet, so saving an XLSX as CSV drops everything except the values of the active sheet.
How to Open an XLSX File Without Excel
- LibreOffice Calc opens XLSX on Windows, macOS, and Linux.
- Google Sheets imports an uploaded XLSX and can export it back.
- Free online viewers show the sheets in a browser, though large files and complex formulas may not display fully.
Common XLSX Problems
- Excel says the file format or extension is not valid. The file is usually damaged, truncated during a download, or has an .xlsx name but a different format inside, such as an old XLS or an HTML export.
- The file will not unzip. The ZIP package is corrupted. Excel's Open and Repair command is the first thing to try.
- A password prompt appears. A protected workbook is encrypted, and without the password the content cannot be read.
How to Compare Two XLSX Files
Two versions of one workbook rarely differ in obvious places. For a quick check, you can
compare two XLSX files online and see which cells changed between them. For regular work with workbooks, the desktop
Spreadsheet Compare and Merge tool compares files on your PC.
How to Merge Many XLSX Files Into One
Copying sheets by hand works for two or three workbooks and stops being practical at fifty. The
Spreadsheet Compare and Merge tool combines many Excel files into one workbook on Windows.
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