"First is that hard disc manufacturers quote the capacity of their decimally, where kilo=1,000 (and mega=1,000 kilo etc), whereas operating systems usually use the binary standard, where kilo=1024 etc. On large modern hard discs this can amount to quite a difference.
Secondly, formatting discs involves creating a filesystem a way of organising the files and folders on the disc (a bit like having table of contents, page numbers and indexes in a book), and this uses up some space. Depending on the filesystem, the amount of space can be considerable.
http://www.makeuseof.com/answers/hard-drives-lose-space-formatting/ "
All perfectly normal.. Think of that space as your file cabinet. There has to be a structure for you to put your files in..