XLS vs XLSX: What's the Difference Between Excel Formats?

XLS vs XLSX is the difference between Excel's old file format and its current one. XLS is the binary format used by Excel 97 to Excel 2003. XLSX has been the default since Excel 2007: it stores the workbook as compressed XML, holds 16 times more rows, and can't contain macros. This guide explains what changes between the two, what you lose when you save as XLS, and how to convert old files safely.

XLS vs XLSX at a glance#

XLSX is the modern default; XLS survives only for compatibility.

The extension is the part of a file name after the dot. It tells Excel which format to expect. A binary file stores data as raw bytes that only a program built for it can read; XML is structured text, which is why so many other tools can read and write XLSX.

What XLS and XLSX files are#

An XLS file is a single binary file in the format Excel used for about ten years. Every Excel version since 97 can open it, which is its one real strength. But it was designed for the computers of the 1990s, and its limits show it.

An XLSX file is a ZIP archive of XML files: one for each sheet, plus files for styles, shared text and settings. Because it is compressed, the same data usually takes less space. Because the format is a published open standard, most modern spreadsheet apps, databases and programming tools can read it directly.

XLSX can't store VBA macros. That is deliberate: a file that can't hold code is safer to open from an email. If a workbook needs macros, Excel saves it as XLSM instead. The XLSX vs XLSM comparison covers macro files in detail, and CSV vs XLSX explains when plain text is the better choice.

The same sheet in XLS and XLSX#

The quickest way to see the difference is to jump to the edge of a sheet. Open a blank sheet and press Ctrl+Down Arrow (Mac: ⌘+Down Arrow), then Ctrl+Right Arrow (Mac: ⌘+Right Arrow).

Now picture a 100,000-row sales export with an XLOOKUP summary and a formatted table. Saved as XLSX, everything is kept. Saved as XLS, the Compatibility Checker warns you that:

• rows after 65,536 will be lost, so about a third of the data disappears;
• the table becomes a normal range;
• XLOOKUP isn't available in Excel 97-2003, so the formula would show #NAME? if recalculated there.

If rows, columns and cell addresses are new to you, the lesson on cells, rows and columns explains how Excel names every cell.

When to use XLSX#

Use XLSX by default. It is the right choice when:

• The file is for people with Excel 2007 or later, which today is nearly everyone, on Windows, Mac, the web or mobile.
• You need space: more than 65,536 rows or 256 columns.
• You use modern features such as tables, slicers, conditional formatting with many rules, or functions like XLOOKUP and FILTER. See Excel 365 vs Excel 2021 vs 2019 for which version has which functions.
• The file goes to other software, such as a database import or a reporting tool, that reads Office Open XML.
• You want a safer attachment. An XLSX file can't carry macros.

Excel for the web also works with XLSX; the desktop vs web comparison covers what each app can do.

When to use XLS, and how to convert it#

Use XLS only when a person or system can't open XLSX, such as very old software that only reads Excel 97-2003 files.

When you open an XLS file in current Excel, the title bar shows [Compatibility Mode]. The old limits stay on, so the file keeps working in old versions. To convert it:

1. Windows: choose File > Info > Convert. Excel saves an XLSX copy and offers to reopen it.
2. Windows or Mac: choose File > Save As (Windows: F12; Mac: ⌘+Shift+S) and pick Excel Workbook (.xlsx).
3. If the old file has macros you need, pick Excel Macro-Enabled Workbook (.xlsm) instead.
4. Close and reopen the new file. The full 1,048,576 rows appear only after reopening.

If you must save as XLS, choose Excel 97-2003 Workbook (.xls) in Save As. Excel runs the Compatibility Checker, which lists what will be lost or changed. On Windows you can run it any time from File > Info > Check for Issues > Check Compatibility. Read the list before you click Continue.

Common mistakes with XLS and XLSX#

These slips cause most file-format trouble:

1. Renaming instead of converting. Changing .xls to .xlsx in File Explorer or Finder doesn't change the format inside. Excel warns that the format and extension don't match.
2. Working in Compatibility Mode without noticing. Data pasted past row 65,536 is refused, and new functions may be flagged. Check the title bar.
3. Not seeing extensions at all. Windows hides them by default: in File Explorer, choose View > Show > File name extensions. On a Mac, turn on Finder > Settings > Advanced > Show all filename extensions.
4. Converting a macro file to XLSX. The macros are removed. Use XLSM.
5. Breaking links between files. A formula like ='[Prices.xls]Sheet1'!B2 still points to the old name after you convert Prices.xls. Update it with Data > Edit Links > Change Source.
6. Counting files with the wrong wildcard. In a list of file names, "*.xls" matches only names that end in .xls, while "*.xls*" also matches .xlsx and .xlsm. The exercise on this page uses the first one.

If you receive data as text files rather than workbooks, the guide to importing CSV files into Excel shows how to keep leading zeros and dates intact.

Our recommendation#

Save everything as XLSX unless you have a specific reason not to. It holds more data, keeps every feature, makes smaller files and can't carry macros. Convert old XLS files when you next edit them, and keep a backup of the original until you've checked the new file. Use XLSM only when a workbook needs macros, and XLS only for software that can't read anything newer.

Practise it#

File formats are part of the Excel basics that job tests expect you to know. Check your Excel basics with the skill check, then practise working with cells, rows and columns in a live spreadsheet that checks each answer instantly. Not sure where you stand? Take the Excel level test to find the right starting point.