I am working on an applescript which includes creating a disk image and copying a folder to it. My script calculates the size the disk image needs to be to fit all the files on it, and then sends a shell command to create and mount the disk image. The problem is that the once the disk image is mounted the capacity is significantly less than the corresponding .dmg file.

(example: mydiskimage.dmg = 10.04 GB, but when mounted it only has a capacity of 9.72 GB, where is the missing 328 MB?)

So my question is where is the missing disk space, and is there a way to calculate how much that is going to be so I can include it when I'm creating the .dmg file?

Here is the applescript command I'm using to create the disk image:

do shell script "hdiutil create -size 10278.1640625m -fs HFS+ -volname \"Converted Clips\" converted_clips.dmg"