Device pixel ratio - How to select a proper size image that looks sharp and display fast on different devices

What is Device Pixel Ratio?

The term device pixel ratio plays the crucial role in different languages’ styling. The definition of Device pixel ratio from MDN:

The devicePixelRatio of Window interface returns the ratio of the resolution in physical pixels to the resolution in CSS pixels for the current display device.

My translation:

Device pixel ratio = (Device physical pixel width) / (Width of a device in a program)

For instance an iPhone12:

  • Physical Width: 1170px
  • CSS width: 390px
  • Device Ratio Pixel: 1170px / 390px = 3

How to select a proper width image

Proper image size = devicePixelRatio * width

If you setup a image with style width:150px, the phone will use 150 * 3 = 450 physical pixel to render, so the proper width of the image should be 450

Common Device Pixel Ratio