Microsoft Excel .xlsx Files: Workbooks and Worksheets

A Microsoft Excel .xlsx file is an Excel workbook: a file that can contain one or more worksheets, along with formulas, formatting, charts, and other spreadsheet content. A worksheet is a single tab inside the workbook, so “worksheet” and “.xlsx file” are related but not interchangeable terms.

Workbook and worksheet: what is the difference?

Think of an .xlsx file as a folder or container for spreadsheet work, and a worksheet as one page within it. When you open a workbook in Excel, the sheet tabs appear along the bottom of the window. A workbook might have one sheet for a monthly budget, or several sheets for separate months, categories, and a yearly summary.

For example, a small shop could keep one workbook called “Sales 2026.xlsx” with worksheets named January, February, and Summary. The monthly sheets might hold individual transactions, while the summary sheet presents totals or a chart. All those tabs are saved together in the same workbook file. The workbook’s file name and extension are visible in the title bar or when you browse for the file; the selected worksheet’s name appears on its tab.

Excel can also include sheet types other than ordinary worksheets, such as chart sheets, which display a chart on its own tab. In everyday use, however, “sheet” usually means a worksheet containing cells arranged in rows and columns. Adding a worksheet does not create a separate file; saving the workbook saves its sheets together.

What the .xlsx extension means

The .xlsx extension identifies the standard, macro-free Excel workbook format introduced with Office 2007. It belongs to the Office Open XML family of formats, standardized as ISO/IEC 29500. The format is not simply a picture of a spreadsheet: it stores workbook information in structured parts that Excel can read and update.

Technically, an .xlsx file is a ZIP-based package containing XML files and related resources. Those parts describe items such as the workbook’s sheets, cell values, formulas, styles, and charts. Images and other resources may be stored as package components as well. Most users should open or save the file through Excel rather than edit these internal parts directly; changing package contents incorrectly can damage the workbook.

Because the format is structured, compatible spreadsheet programs can often read and write .xlsx files without using Excel itself. Compatibility is not a guarantee that every feature will behave identically, though. A program may interpret a formula differently, omit a newer Excel feature, or change formatting when it saves the file.

What an Excel workbook can contain

An .xlsx workbook can store far more than typed values. Cells may contain text, numbers, dates, formulas, or references to other cells. Excel also saves presentation and analysis features, which is why an ordinary workbook can be useful as a report, tracker, or data model as well as a basic grid.

Worksheets and cell data: A worksheet has rows and columns of cells. In modern Excel, a worksheet can have up to 1,048,576 rows and 16,384 columns, with the final column labeled XFD. Practical limits may be lower depending on computer memory and workbook complexity.
Formulas and functions: Cells can calculate results from other cells, and formulas can refer to cells on other sheets in the same workbook. The displayed result is generally recalculated by Excel when relevant inputs change.
Formatting and tables: Fonts, number formats, cell colors, structured Excel tables, conditional formatting, and data validation help present information and guide data entry.
Visual and analysis features: Workbooks can contain charts, PivotTables, filters, and other tools for summarizing or presenting information. Some advanced features may depend on the Excel version or connected services used to create them.
Workbook-level information: The file can preserve sheet names and order, defined names, links, print settings, and other settings. A particular workbook may contain only a small subset of these features.

A useful distinction is that the file extension tells you the general file format, not what is inside the workbook. Two .xlsx files can look completely different: one might be a plain list, while another contains dozens of sheets, charts, and formulas.

Opening, creating, and saving an .xlsx file

In Excel for Microsoft 365 on Windows, open an existing file by choosing File > Open and browsing to it, or open it from File Explorer. To start a workbook, choose File > New > Blank workbook. Excel normally saves a new workbook in the current default format, which is .xlsx.

To choose the format explicitly in Windows, use File > Save As > Browse, then select Excel Workbook (*.xlsx) in the file-type list and save. If you are working on a Mac, use File > Save As and choose the Excel workbook format in the file-format selector; the dialog’s layout differs from Windows. Excel for the web also supports working with Excel workbooks, though some desktop features or file operations may not be available there.

When you add or rename a worksheet, you are changing the open workbook, not creating a new .xlsx file. Use the plus button beside the sheet tabs to add a sheet, or right-click a tab for sheet-management options. Save the workbook afterward using Ctrl+S on Windows or Command+S on Mac. If the file is stored in a cloud location with AutoSave available and enabled, changes may save automatically, but it is still sensible to confirm that the workbook has finished saving before closing it.

How .xlsx compares with other spreadsheet formats

Choosing a format matters when a workbook contains macros, when another application must read it, or when you need to exchange data as plain text. The extension helps identify the format and its intended capabilities.

.xlsx: The common modern Excel workbook format. It supports ordinary spreadsheet content but does not store VBA macros.
.xlsm: An Excel macro-enabled workbook format that can store VBA macros. Use it when a workbook needs those macros and the recipients can safely use them.
.xls: The older Excel binary workbook format used by earlier Excel versions. It can be needed for legacy compatibility, but it has different feature and capacity limits from modern formats.
.csv: A text format for tabular data, typically representing one sheet at a time. It does not preserve workbook features such as multiple sheets, formulas as formulas, cell formatting, or charts.

A common mistake is to rename a file’s extension to change its format. Renaming report.csv to report.xlsx does not convert its contents into an Excel workbook. Use Excel’s Save As or export options to create a real file in another format. Also note that if you save a macro-enabled workbook as .xlsx, Excel warns that macros cannot be retained in that format; do not proceed if the macros must remain available.

Compatibility and sharing

Excel is the most predictable choice for a workbook created with Excel-specific features. Recent versions of Microsoft Excel, including Excel for Microsoft 365, can open .xlsx files. Excel for the web can also open and edit many of them. Other spreadsheet applications, including LibreOffice Calc, may support the format, but a round trip—opening, editing, and saving in a different program—can alter elements that are not fully supported there.

Before sharing a workbook, consider what the recipient needs to do with it. If they need to edit formulas and use multiple sheets, sending the .xlsx workbook is generally more useful than sending a CSV. If they only need a simple data extract for importing into another system, CSV may be appropriate, but check how that system expects dates, delimiters, and text encoding to be represented.

For files shared with people using older software, keep a copy of the original and check for compatibility warnings when saving. If a recipient reports that a feature is missing, ask which spreadsheet program and version they use, and whether the issue appears in the original file or only after they save it. A preview or exported PDF can help preserve the appearance of a report, but it will not replace an editable workbook.

Common problems and safe handling

If Excel cannot open an .xlsx file, first check that the file finished downloading or copying and that its name really ends in .xlsx. A file may have the wrong extension, be incomplete, or be damaged. Try opening it from Excel using File > Open, and, if possible, compare it with another copy or ask the sender to send it again. Do not assume that changing the extension will repair it.

If a workbook opens but looks different, the cause may be a font that is unavailable, a feature unsupported by the program, a calculation setting, or a change made during conversion. Check the file in Excel if available and review any compatibility or recovery messages rather than immediately overwriting the only copy. Save a separate copy before making substantial repairs or format conversions.

An .xlsx file does not contain VBA macros, but that does not mean every workbook is automatically safe. It can contain formulas, external links, embedded content, or data that you did not expect. Only open files from sources you trust, be cautious about enabling external content or following links, and review unexpected warnings. If a workbook asks to update links to another file, consider whether you recognize the source before allowing it to retrieve information.

Frequently Asked Questions

Is an .xlsx file the same as an Excel worksheet?
No. An .xlsx file is a workbook, which can contain one or more worksheets and other workbook content. A worksheet is an individual tab of cells within that file.

Can I open an .xlsx file without Microsoft Excel?
Often, yes. Excel for the web and compatible spreadsheet applications can open many .xlsx files. Complex or newer Excel features may not transfer perfectly, so check the workbook after opening or editing it elsewhere.

Does .xlsx support macros?
No. The standard .xlsx format does not retain VBA macros. For a workbook that needs VBA, use the macro-enabled .xlsm format and follow your organization’s security rules for macros.

How do I convert an Excel file to .xlsx?
Open the file in Excel, choose File > Save As, and select Excel Workbook (*.xlsx) as the file type. Review any warning about unsupported content, especially if the source is a macro-enabled workbook, because features may be removed when changing formats.

Can an .xlsx file contain multiple sheets?
Yes. A workbook can contain multiple worksheets, and the sheet tabs let you move among them. The sheets are saved together in the same workbook file unless you separately copy or export content to another file.

Try it: the Date Difference Calculator: days, months, years and weekdays between two dates, with the DATEDIF formulas.

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Sources: Function behaviour and menu paths: Microsoft Support documentation for Excel. Method & sources

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