How do I open a .dmg file?

On Windows use 7-Zip (to inspect contents only); on macOS use DiskImageMounter (built in); on Linux use 7z x (p7zip, to inspect contents only). How Mac software is distributed — a disk image you mount and drag an app out of.

Can I convert a .dmg file?

Yes. It is usually converted to .iso, .img or .zip, either by exporting from one of the programs listed above or with a format converter.

.dmg files

.dmg file

Apple Disk Image

How Mac software is distributed — a disk image you mount and drag an app out of.

What opens a .dmg file

Windows: 7-Zip (to inspect contents only)
macOS: DiskImageMounter (built in), Disk Utility (built in)
Linux: 7z x (p7zip, to inspect contents only), dmg2img

What a .dmg file is

DMG is a macOS disk image, often compressed and sometimes encrypted, that mounts as a virtual drive when you double-click it. The convention is to drag the app inside to your Applications folder and then eject the image. On Windows, 7-Zip can list and extract the contents, but Mac applications will not run there, so extracting one is only useful for retrieving non-Mac files inside.

Converting it

A .dmg file is commonly converted to .iso, .img or .zip. It is a binary format, so a text editor will show unreadable characters rather than its contents.

Details

Extension: .dmg
Full name: Apple Disk Image
Category: Disk images
MIME type: application/x-apple-diskimage
Created by: Apple
Format: Binary

Common questions

How do I open a .dmg file?: On Windows use 7-Zip (to inspect contents only); on macOS use DiskImageMounter (built in); on Linux use 7z x (p7zip, to inspect contents only). How Mac software is distributed — a disk image you mount and drag an app out of.
What is a .dmg file?: Apple Disk Image. DMG is a macOS disk image, often compressed and sometimes encrypted, that mounts as a virtual drive when you double-click it. The convention is to drag the app inside to your Applications folder and then eject the image.
Can I convert a .dmg file?: Yes. It is usually converted to .iso, .img or .zip, either by exporting from one of the programs listed above or with a format converter.

.iso — ISO Disc Image A byte-for-byte copy of a CD, DVD or installer disc in one file.
.vmdk — Virtual Machine Disk VMware's virtual hard disk — the contents of a whole virtual computer.
.cue — Cue Sheet A small text file describing the track layout of a .bin disc image.

Sources

Media Types Registry — IANA
Official vendor product documentation — At One Place

How these figures are compiled and checked