As stated in the CSS3 values specification, the unit px
represents an absolute physical length and is intended to correspond to real-world dimensions:
The reference pixel# denotes the visual angle of one pixel on a device with a pixel density of 96dpi and positioned at a distance from the observer equivalent to an arm's length. Assuming an arm's length of 28 inches, this visual angle comes out to about 0.0213 degrees. Therefore, reading at arm's length, 1px equates to approximately 0.26 mm (1/96 inch).
This implies that the device itself should adjust your px
measurement based on the display - for instance, on a 4k screen, you may observe 4 physical pixels for each CSS pixel. However, this behavior can be configured by the user through the operating system settings.
Setting a fixed width for a website is generally discouraged - what happens when the browser window is not maximized? How does it render on mobile devices? It is advisable to utilize relative length units such as %
and em
to ensure your layout remains adaptable and responsive across various scenarios.