dpi is irrelevant on screen. It only matters when printing.
ppi and dpi are often used interchangeably when discussing screens. This happens in places like the Android documentation, where screens are described in terms of dpi... and in W3C specifications which refer to screens... various specifications relating to HTML and CSS refer to dpi, particularly with respect to images. This is because CSS is not specific to screens, and can also be applied to print media... I will use "ppi" when referring to screens and reserve "dpi" for referring to print...
CSS does not use PPI; it only uses DPI. Section 6.4 of css-values-3 lists the following units: dpi... dppx Dots per px unit. For the purposes of CSS and Media Queries, a single "dot" always corresponds to a single physical pixel, never a DIP or CSS pixel, hence the dppx unit. For example, a scale factor of 200% or device pixel ratio (non-standard) of 2.0 is equivalent to 2 dppx.
- all screen sizes supported by Android (as small as 426dp x 320dp)
- 320dp: a typical phone screen (240x320 ldpi, 320x480 mdpi, 480x800 hdpi, etc).
- 480dp: a tweener tablet like the Streak (480x800 mdpi).
- 600dp: a 7” tablet (600x1024 mdpi).
- 720dp: a 10” tablet (720x1280 mdpi, 800x1280 mdpi, etc).
This category has the following 2 subcategories, out of 2 total.