How to open .dmg files

Mac disk image files explained, with instructions for opening them on macOS and Windows.

Updated April 2026 6 min read Beginner
Quick answer
  • Mac: double-click the .dmg → drag the app to Applications → eject the DMG.
  • Windows: DMG files are Mac-only. Use 7-Zip to peek inside, but you generally can’t run the Mac apps they contain.
  • Password-protected DMG? Mounting it prompts for the password automatically on Mac.

What is a DMG file?

A DMG (disk image) is Apple’s standard format for distributing Mac software. When you download a Mac app, it usually comes as a .dmg — think of it as a virtual USB stick containing the app plus a pretty installer background and an alias to Applications.

DMGs are Mac-native. On Windows they’re essentially useless for running software (Mac apps don’t run on Windows), but you can still peek inside the archive if needed.

Open a DMG on Mac

  1. Double-click the .dmg macOS mounts it — a new icon appears on your desktop and in Finder’s sidebar.
  2. A Finder window opens Usually showing the app icon and an Applications shortcut.
  3. Drag the app into Applications This is the install step. The app is now on your Mac.
  4. Eject the DMG In Finder, click the eject icon next to the DMG in the sidebar. Or drag its desktop icon to the Trash.
  5. Delete the .dmg file You don’t need it anymore once the app is installed.
App says “can’t be opened because it’s from an unidentified developer”?Right-click the app in Applications → Open. macOS will ask for confirmation once; after that it runs normally.

Password-protected DMG

Some DMGs (including ones you create with Disk Utility) are encrypted. Double-clicking prompts for the password automatically — just enter it, click OK, and proceed normally.

If macOS says “can’t mount disk image” with no password prompt, the DMG may be corrupted. Try hdiutil attach ~/Downloads/file.dmg in Terminal for a more detailed error message.

Open a DMG on Windows

Windows has no built-in DMG support. You can extract the contents with 7-Zip — but for most DMGs that means getting a Mac .app bundle, which Windows can’t run. It’s only useful if the DMG contains documents or images.

  1. Install 7-Zip from 7-zip.org.
  2. Right-click the .dmg → 7-Zip → Extract Here You’ll get a folder with the DMG’s contents.
  3. Look for usable files PDFs, images, and some cross-platform installers may be inside. Mac .app bundles will not run.
Need Mac software on Windows?Most Mac apps also have Windows versions. Check the developer’s website for a .exe or .msi installer instead of trying to force a .dmg to work.

Frequently asked questions

Can I convert a DMG to an ISO?

Yes, on Mac, using Terminal: hdiutil convert yourfile.dmg -format UDTO -o converted.iso. Rename the .cdr it produces to .iso. On Windows, tools like DMG2IMG can do this, but results are hit-or-miss.

The DMG mounts but the app won’t run

Check the app’s minimum macOS version (right-click app → Get Info). Apps built for macOS 13+ won’t run on older systems. Intel-only apps won’t run on Apple Silicon Macs without Rosetta 2 installed.

What does “checksum error” mean when opening a DMG?

The file didn’t download completely or was corrupted in transit. Re-download from the original source.