A .dmg is just the installer image for a Mac app. Once the app is in Applications, the .dmg is dead weight.

Short answer: open Finder's Downloads folder, search for .dmg scoped to Downloads, select all, and move to Trash. Repeat for .pkg installers.

Why DMGs stick around

A disk image is basically a virtual CD. When you download an app from outside the Mac App Store, you mount the .dmg, drag the app into Applications, and eject.

Most people stop there. The .dmg itself, often 1-5 GB for something like Photoshop or Office, sits in Downloads untouched. A couple of years of that and Downloads can hold 20-50 GB of useless installer images.

Bulk deleting in Finder

  1. open Finder
  2. click Downloads in the sidebar
  3. type .dmg in the search bar
  4. under the search bar, switch the scope from This Mac to Downloads
  5. press Command + A to select everything
  6. move to Trash and empty it

Repeat the same sweep with .pkg for older installer packages.

When to keep one

Keep a .dmg only if the app cost money and the license was tied to that installer, or the app is no longer available for download. In every other case, the installer is pure overhead.

Better next routes

If the drive is still heavy after installer cleanup, continue with How to Find Large Hidden Files on Mac.

For the broader framing, use What Is Purgeable Storage on Mac?.