What’s the easiest way to increase the capacity of a DMG file?

Johnny March 15, 2015

What’s the easiest way to increase the size/capacity of a DMG file?

I would like to expand or increase the size of an existing password-protected DMG file. It’s currently 100MB. How do I expand it to a larger size, say 2GB?

After expanding, will it occupy 2GB of space on my hard drive or flash drive?

  1. Jan F.
    March 17, 2015 at 5:34 pm

    Assuming it is a standard read-write image all you have to do is:
    open up Disk Utility (you can find it via Spotlight)
    drag & drop your DMG file into the white area on the left hand side, where your Macintosh HD is also shown
    select the DMG file and at the top click the "Resize Image" button (or via the Menu Images > Resize)

    A Disk Image will always take up as much space as you sized it. If you make it 2GB it will take up 2 GB of space on your hard drive or flash drive. A sparse images will grow according to it's contents with the selected size being the limit.

    • Jackson
      March 20, 2015 at 3:58 am

      That doesn't work if the DMG is password-protected.

    • Jan F.
      March 20, 2015 at 7:02 am

      It does work. I have tested that under 10.6.8, 10.7.5 as well as 10.10 Yosemite.
      Disk Utility will prompt you for the encryption password. When entered correctly it will unlock the DMG file and you are able to resize it.

      My guess would be that the image you tried resize was not a read-write image but a read-only or compressed Disk Image. Both are literally "read only" and need to be converted before you can do any modification to them, regardless of any password protection.