I created an ISO image of a bootable USB stick with a size of 32 GB. Only approximatly 4 GB of the 32 GB were used.

The created iso size seems to use the full 32 GB not only the 4 GB.

Is there a way (windows tool, windows command line) to shrink the iso?


I made a mistake. I want to shring img images.

They were created with USBIT (USB Image Toolkit).

No idea what the comment of @Ramhound meant but it contained nothing weirder than a Windows 7 Backup stick (and the few files that were backuped after a complete fresh install of Win 7).

I have the same issue with Win 32 Disk Imager images used to create backups of SD cards for e.g. Raspberry Pi.

Workaround (failed)

Not exactly what I wanted but I found the tool imgtoiso. With that I was able to shrink (by converting img to iso).

The .img of my 32 GB Win 10 Backup stick had 29.2 GB (31 457 280 000 Bytes)

The .iso (img to iso) now has 352 KB (360 448 Bytes)

Well, thats much easier to store on an external HDD but when using rufus to copy the iso back to the usb stick it showed the iso was not working

  • 2
    Unless you did something weird, you should simply be using 4 GB of a 32 GB storage device. All you would do is create a folder on the storage device, place files in that folder, there a reason you cannot do that? – Ramhound Jun 2 '17 at 15:58
  • What tool(s) did you use to create the ISO? – music2myear Jun 2 '17 at 16:11
  • @music2myear usbit – monty Jun 4 '17 at 13:17
  • An .ISO of 352 Kb in size is unlikely to contain anything useful. The ISO format is uncompressed (but even if it wasn't, 4GB to 0.3Mb is a compression ration achievable only by a file shredder). – LSerni Jun 20 '17 at 17:35
  • @LSerni in fact, it isn't usefull, the iso did not work when i tried to copy it with rufus. – monty Jun 20 '17 at 20:39

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