How to Open a DMG File on a Mac

By Garrett Genet

A .dmg file is a copy of a physical disk, such as a CD or DVD, contained in a single file. The file extension means "Disk Image" and is proprietary to Apple. The operating system treats this file as it would a physical disk. Normally OS X will automatically mount a .dmg file when you double click it, however should this fail you can manually mount an image using tools that come with the operating system.

Things You'll Need

  • Macintosh OS X

Step 1

Open "Disk Utility" from your Applications list. It should be in a folder called Utilities.

Step 2

Click "Mount" at the top and select the .dmg file you want to open. Once mounted it will appear on your desktop as an icon.

Step 3

Double-click the icon of the image to open it.

Tips & Warnings

  • Alternatively, you can drag the .dmg file onto the icon for Disk Utility; it should automatically mount the image.
  • Earlier versions of Apple's operating systems use .img and .smi file extensions; they cannot read the .dmg file extension.