I'm converting a website for mobile browser, and i'm using my Lumia 520 for test it. The technical specs of the smartphone says that it have a width of 480px but if i set this value for the body width of the website, i see that it goes out of the screen!

So i tryied to set body to width:100% and throught jquery see what is the automatic value that is set, the result is 320px..

Why this difference and how to know the exact resolution of a smartphone??