I have only used up 2.1 gigs on my iPhone 4s, but my storage settings say I have used 5.4?

Why is this happening? I have definitely not used 5.4 gigabytes; I have checked everything on my phone.

Would someone please explain this?

IN the Setting, you can see how much space each app and program takes up. There ya go. You might decide to remove some that you do not use - including ones you DID remove, but have left retrieval info, in case you want to add them again from where they are stored in iTunes on your computer. You'd have to remove them from THERE, too, for them to be really gone. This is like running the Tree programs on your computer, to see where all kinds of junk is hogging your drive space.