Mac storage basics · Finding big files, Downloads and the Trash
Can I delete .dmg files after installing an app?
Short answer: Yes — once the app is in Applications and the disk image is ejected, the .dmg isn't needed. The same applies to used .pkg installers and unpacked .zip files.
Yes. A .dmg file is just the disk image the app arrived in. Once you've dragged the app into Applications (and ejected the mounted disk image), the .dmg isn't needed to run the app. Delete it, or keep a copy elsewhere if the download is hard to get again.
The same goes for .pkg installers after installation, and .zip files you've already unpacked.