Clean installation... not so clean

Hi,

I've got the Macbook Air (128GB, Mountain Lion) and when I initially bought the Air, I got 120GB free space. The total memory is 128 GB. I understand that the OS takes about 8GB. Which is logical. However, when I attempted a clean installation I now only have 109 GB. Please advise. What didn't I delete?

It's not memory, it's storage. I'm not being pedantic, it's important to use proper terminology or people trying to help you end up going down a rabbit hole into nowhere because of mis-communication.

On the space, I can't say, but have you checked to make sure the trash can is emptied? And how did you do the clean installation? Did you repartition and/or reformat the drive, or did you just run the installer and point to the drive? It makes a difference on which you did.