Device pixel ratio.

The dpr parameter provides a means to multiply image dimensions in order to translate logical pixels (also 'CSS pixels') into physical pixels. The device pixel ratio is therefore the ratio between physical pixels and logical pixels.

It is usually possible for client-side software to query the host system to determine the DPR of the display the user is viewing. In web browsers, this is available as the Window.devicePixelRatio variable in JavaScript. The iPhone 5 reports a device pixel ratio of 2, because the physical linear resolution is double the logical resolution.

  • Physical Resolution: 960 x 640
  • Logical Resolution: 480 x 320

Other devices report varying device pixel ratios, including non-integer ones. For example, the Nokia Lumia 1020 reports 1.6667, whereas the Samsung Galaxy S4 reports 3.



value may be any number between 1 and 10.


Click the links to view the transformed image using a demo Fastly IO service.

Example usageDescription
?width=200&dpr=2Resize the width to 400px (200 CSS pixels for screens with a device pixel ratio of 2)