Only 7.9 Gigs of Music but on itunes it says its 9.3 Gigs iPhone 4

Hi this is my first time posting on the apple forums so Im not sure if this is in the right section or not. I was just hoping someone could help me with this little problem of mine.
I recently just got an iPhone 4 16 GB, and before that I had a 80 GB iPod. On my iPod all of my music came up to 7.9 GB and now that Ive transferred it all to my iPhone it says its 9.3 GB instead of only the 7? Even on my computer it says that all my music only comes up too 7.9 GB. Also every time I plug my iPhone in on iTunes it says it has 7.9 of music and then it jumps back up to the 9.3.
I dont understand why it does this or how to even fix it.
Any Help would be greatly appreciated.
iOS 4