What is a DMG File?

How to Open, Edit, & Convert DMG Files

Official DMG icon image
© Apple Inc.

A file with the DMG file extension is a Mac OS X Disk Image file, which is basically a digital reconstruction of a physical disc.

For this reason, a DMG is often the file format used to store compressed software installers instead of having to use a physical disc. You'll most likely only see them when downloading Mac OS software from the Internet.

Versions of Mac newer than OS X 9 support DMG files, while the older Mac OS Classic uses the IMG file format for the same purpose.

How To Open a DMG File on a Mac

DMG files are intended for Macs, so opening one on a Mac is very simple.

A DMG file is "mounted" as a drive and is treated by the operating system as if it were a physical disc, making it really easy to view the contents of. The software you download for your Mac in a DMG format can be opened like any other file on a Mac, and then the setup program can be run to install the software.

How To Open a DMG Files in Windows

A DMG file can certainly be opened in Windows, but that doesn't mean you can actually use anything you find within it.

For example, say a DMG file isn't just storing compressed files like images and videos but is instead holding a software program. You can extract, or open, the DMG file in Windows using one of the programs I mention below, but you can't actually execute the program and use it like you would another Windows application. To use the same program in Windows, you need to download the Windows version, not the Mac DMG version.

However, assuming the DMG file just contains files like images or videos (which are likely in a format that's also compatible with Windows), you should have no problem using one of the below programs to view them.

Windows can open a DMG file with any compression/decompression program that supports the format.

PeaZip and 7-Zip, both free, support opening DMG files in Windows. 

Tip: If you have trouble opening DMG files by double-clicking on them, even if you have PeaZip or 7-Zip installed, try right-clicking and using the context menu. For example, 7-Zip opens DMG files with the 7-Zip > Open archive option.

DMG Extractor (the paid version) is helpful if you need to do more with DMG files than just uncompress them.

SysTools DMG Viewer is great if all you want to do is look to see what's in the DMG file. That program is completely free.

A free tool called dmg2iso will convert the DMG image file to an ISO image file, which is much more usable in Windows. If you need to mount a DMG file in Windows, but don't want to convert it to ISO first, a few programs do support this, like WinCDEmu, Virtual CloneDrive, and Prismo File Mount Audit Package. Newer versions of Windows support ISO mounting natively.

How To Convert a DMG File

As I mentioned above, dmg2iso can be used to convert DMG to ISO. dm2iso is a command-line tool, so you may need to reference the download page for instructions on the syntax and other rules. Also on the download page is a DMG to the IMG tool if you need to convert the file to an IMG file instead.

AnyToISO works the same way as dmg2iso but is much easier to use. The program is free but only for files that are no larger than 870 MB.

Some free file converters can convert DMG files to a variety of other archive formats, like ZIP, 7Z, TAR, GZ, RAR, and others. CloudConvert and FileZigZag are two notable examples.

Note: Again, just because you can extract a DMG file in Windows, or even convert a DMG to a Windows-readable format, doesn't always mean that the contents of the DMG file will suddenly become compatible with Windows. The only way to use a Mac program or a Mac video game in Windows is to download the Windows-equivalent version.

If there isn't one, then neither converting nor extracting, a DMG file will be of any use.