How to make page width equal to screen width in Opera Mobile, iOS, Android etc

Such browsers as Opera Mobile, iOS browser, Android browser开发者_StackOverflow (last two use webkit engine) emulate lager device's screen, than it is. For example: real device's screen width is 480px, but Opera Mobile shows the page, like the screen is 850px width.

How i can prevent such browsers from emulating larger device's screen size, and make them to display web page as wide, as real device's screen?

Use <meta name="viewport" />

<meta name="viewport" content="width=device-width;" /> in the head should set the viewport to the device width