XLSM vs XLSX: What's the Difference?
(And Why It Matters for Macros)

You've seen both file extensions sitting in folders. They look the same. They open in Excel the same way. But the moment macros are involved, XLSM and XLSX are completely different formats — and mixing them up will silently delete weeks of VBA code.

This guide explains the technical distinction between the two formats, when each one is appropriate, and exactly what happens when converters handle them incorrectly.

The Technical Difference

Both XLSX and XLSM are Open XML formats — ZIP archives with XML files inside. You can rename either to .zip and extract it to see the raw structure. But the contents differ in two critical places:

What's Inside Each ZIP Archive

Rename any Excel file to .zip and extract it. Here's what you'll find:

XLSX structure (no macros possible):

workbook.xlsx/
├── [Content_Types].xml          ← no vba entry
├── _rels/
├── xl/
│   ├── workbook.xml
│   ├── worksheets/
│   ├── styles.xml
│   └── sharedStrings.xml
└── docProps/

XLSM structure (macros live here):

workbook.xlsm/
├── [Content_Types].xml          ← includes vbaProject entry
├── _rels/
├── xl/
│   ├── workbook.xml
│   ├── worksheets/
│   ├── styles.xml
│   ├── sharedStrings.xml
│   └── vbaProject.bin           ← ALL your VBA code is here
└── docProps/

The vbaProject.bin file is a Compound Document Binary Format blob that stores the entire VBA project — every module, every class, every UserForm. When a converter saves as XLSX, it simply omits this file and removes the reference from [Content_Types].xml. The macros don't transform or migrate — they vanish.

When Online Converters Destroy Your Macros

This is where the real damage happens. Tools like CloudConvert, Zamzar, iLovePDF, and Smallpdf all perform server-side conversions using LibreOffice or similar engines. When they convert XLSM files, the pipeline does one of two things:

1. Export to target format, drop vbaProject.bin — the macro code is silently deleted with no warning
2. Re-encode as XLSX internally but keep the .xlsm extension — the file looks like XLSM but the macros are gone; Excel opens it without error and you discover the loss hours later

Neither scenario gives you an error. Neither scenario gives you a warning. You get a clean file back with zero VBA code inside.

The Four Excel Macro Formats Compared

XLSM isn't the only macro-capable format. Here's how all four relate:

When to Use Each Format

Use XLSX when:

• Your workbook has zero VBA code
• You're sharing with people who may flag macro warnings as security risks
• You're uploading to SharePoint, Teams, or OneDrive for co-authoring
• You're importing into Google Sheets
• You want the smallest possible file size

Use XLSM when:

• The workbook requires VBA modules, event handlers, or UserForms to function
• You're distributing to users who will enable macros in a controlled environment
• You're building tools for internal use within an organisation
• You need to preserve macro code between sessions

Use XLSB when:

• The workbook is very large (>10MB) and open/save performance matters
• You don't need to inspect the raw XML (forensic auditing, version control)
• You still need full VBA support but want the binary format's speed advantage

Converting XLSM → XLSX Safely (Without Macro Loss)

If you need to share an XLSM file with someone who can't enable macros, the safe workflow is:

1. Export VBA modules first. In the VBA editor (Alt+F11), right-click each module → Export File. Save as .bas (standard modules), .cls (class modules), or .frm (UserForms).
2. Create a macro-free copy. File → Save As → Excel Workbook (.xlsx). This is your sharing copy — no macros, fully compatible.
3. Keep the XLSM original. Never overwrite it. The XLSX is a derived artefact, not the master.
4. Document what's lost. Add a README worksheet to the XLSX noting which functionality requires macros and where to find the XLSM original.

How to Check if a File Has Macros Before Converting

Before you hand a file to any converter, check whether it contains VBA code:

Option 1 — In Excel: Alt+F11 opens the VBA editor. If the Project Explorer shows modules with code, macros are present.

Option 2 — Free browser tool: Drop the file into the XLSM Macro Inspector — it reads the ZIP structure client-side and lists every VBA module name and line count before you convert anything. No upload required.

Option 3 — Command line (Windows PowerShell):

Add-Type -Assembly System.IO.Compression.FileSystem
$zip = [System.IO.Compression.ZipFile]::OpenRead("workbook.xlsm")
$hasMacros = $zip.Entries | Where-Object { $_.Name -eq "vbaProject.bin" }
if ($hasMacros) { "Has macros" } else { "No macros found" }
$zip.Dispose()

Summary: The Critical Difference

Related Guides

• How to Convert XLSX to XLSM and Keep Macros
• VBA Macros Lost After Conversion — Recovery Guide
• Batch Convert Excel Files While Keeping Macros
• XLSB to XLSM Converter Guide