A blog by Devendra Tewari

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Have the screen resolution (width and height) in pixels and the diagonal length in inches, and want to calculate the PPI? Pretty simple really. The iPad 4 has a screen resolution of 2048 by 1536 pixels, and a diagonal length of 9.7 inches.

We can calculate its PPI as

The calculation above was performed using the wonderful MyScript Calculator, and the result captured by taking a screenshot.

The same formula can be written, expressed using \(\LaTeX\), in a more generalized form as \(\sqrt{w^2 + h^2} \over L\). Where, \(w\) is the screen width in pixels, \(h\) is the screen height in pixels, and \(L\) is the diagonal length of the screen in inches.