title: How to calculate device pixel ratio
body: <p>I would like to know how the -webkit-device-pixel-ratio is calculated. I had already <a href="https://www.quirksmode.org/blog/archives/2012/06/devicepixelrati.html" rel="noreferrer">read this</a>. Yet I am unable to understand it clearly.
  I would also like to know if there is a list of which devices use which pixel ratio. The android website says</p>
  
  <blockquote>
    <p>The Android Browser and WebView support a CSS media feature that allows you to create styles for specific screen densities—the -webkit-device-pixel-ratio CSS media feature. The value you apply to this feature should be either "0.75", "1", or "1.5", to indicate that the styles are for devices with low density, medium density, or high density screens, respectively.</p>
  </blockquote>
  
  <p>but I found that we need to use  -webkit-device-pixel-ratio=2 to make a web application compatible on 768 x 1280 resolution screen.</p>