CSS px is an Angular Measurement
http://inamidst.com/stuff/notes/csspx
The “px” unit in CSS doesn’t really have anything to do with screen pixels, despite the poorly chosen name. It’s actually an non-linear angular measurement. The formulæ to convert between radians and px are as follows:
radians = arctan(px/5376) 2
px = 5376 tan(radians/2)
Using this, you can work out the apparent angular widths of things in pixels quite easily. The moon from earth is about 24.3px wide, for example. The Eiffel Tower from a mile away is about 550.5px tall. That means that when you do “{ width: 24.3px }” in CSS 2.1, you’re making something as wide as the moon looks to be.
















