What is the XLTX file format?
An .xltx file is a Microsoft Excel Open XML Workbook Template - a spreadsheet template that serves as a reusable starting point for new workbooks. It belongs to the Office Open XML (OOXML) family of formats standardised as ECMA-376 and ISO/IEC 29500, introduced with Microsoft Office 2007.
When you open an .xltx in Excel, the application creates a new unnamed .xlsx workbook pre-loaded with the template's styles, formulas, column widths, headers, and any pre-entered data - the original .xltx file itself is never modified. This behaviour distinguishes templates from ordinary workbooks.
Internally, .xltx is a ZIP archive (an OPC - Open Packaging Conventions - package) containing UTF-8 XML part files: xl/workbook.xml defines the workbook structure, xl/worksheets/sheet1.xml holds pre-filled cell data, xl/styles.xml stores number formats and cell formatting, and [Content_Types].xml identifies the package as a spreadsheet template rather than a regular workbook. Renaming .xltx to .zip exposes the full XML structure.
.xltx is the macro-free template format. The macro-enabled equivalent is .xltm, and the legacy binary template is .xlt. An .xltx file cannot store VBA macros - Excel will warn and strip them if present on save. The format is supported by Microsoft Excel, LibreOffice Calc, Apple Numbers, Google Sheets, and most modern spreadsheet applications.
Security & safety
RISK: LOWXLTX cannot contain VBA macros (those require XLTM). Risks are limited to external data links (web queries, Power Query) embedded in templates that auto-refresh on open. Excel's Protected View applies to XLTX from internet/email sources - leave it enabled.
Format details
in a nutshellPrograms that open XLTX files
Windows4 apps
Microsoft Excel
Paid Double-click opens a new workbook based on the template (original is not modified). To edit the template itself: File > Open, then select the .xltx. 
LibreOffice Calc
Open-source File > Open to load the template directly as an editable document. Save As XLSX to create a workbook copy. 
WPS Office Spreadsheets
Freemium Open the XLTX; WPS treats it similarly to Excel - creates a new sheet copy.
SoftMaker FreeOffice (PlanMaker)
Free Open with PlanMaker; note that PlanMaker Viewer is discontinued - use FreeOffice. 
macOS3 apps
Linux1 app
LibreOffice Calc
Open-source File > Open; complex styles and conditional formatting may render differently. 
Google Sheets
Free Upload to Google Drive; right-click > Open with Google Sheets. Download as XLSX, ODS or CSV.
Excel for the web
Free Upload to OneDrive; click to open in Excel Online. Free Microsoft account required. Technical details
deep spec| Container | ZIP archive / OPC (Open Packaging Conventions) |
| Encoding | Binary (ZIP wrapper) + UTF-8 XML part files inside |
| Compression | DEFLATE per entry |
| MIME type | application/vnd.openxmlformats-officedocument.spreadsheetml.template |
| Standard | ECMA-376 5th ed. (2021) / ISO/IEC 29500 Transitional or Strict conformance |
| Key internal files | xl/workbook.xml, xl/worksheets/sheetN.xml, xl/styles.xml, [Content_Types].xml |
| Template behavior | Opening in Excel creates a new unnamed workbook; the original .xltx is never modified |
| Macro support | None - macro-enabled equivalent is .xltm; VBA is stripped on save as .xltx |
| Magic bytes | 50 4B 03 04 ("PK") at offset 0; distinguished from .xlsx by [Content_Types].xml declaring spreadsheetml.template |
| Encryption | Password-protected files use OOXML Agile encryption (CryptoAPI) |
| Typical file size | 10 KB - 10 MB depending on styles, images, and charts |
| Integrity | ZIP CRC-32 per entry |
| Cross-platform support | Windows (Excel), macOS (Excel/Numbers), Linux (LibreOffice Calc), Web (Excel Online) |
| Legacy equivalent | .xlt - Excel 97-2003 binary template format |
| Released | 2007 (Microsoft Office 2007, Excel 12.0); standardised ECMA-376 (2006) / ISO/IEC 29500 (2008) |
| Latest version | ECMA-376 5th edition (2021) / ISO/IEC 29500:2016 |
| Open standard | Yes · royalty-free |
| Specification | ecma-international.org |
XLTX conversions
Community Q&A
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