How Do High-DPI Devices Like Retina Displays And 1080p Phones Handle Pixels In Media Queries?

For example, how many pixels does the iPhone with a Retina display appear to a media query? Is it 320 pixels or 640 pixels? If it's 640 pixels, how can a website deal with differen

Solution 1:

Retina devices like the iPhone and iPad usually use 2 device pixels = 1 CSS pixel. So a media query like this:

@media all and (max-width: 320px) {
}

actually will target an iPhone (portrait), even though it is 640 device pixels wide.