Ecco un paio di utili calcolatori online:
DPI Calculator / PPI Calculator
(© 2004-2017 Sven Neuhaus <sven@sven.de>. All rights reserved.)
https://www.sven.de/dpi/
FOV / Field of view / Field of vision calculator
(© 2016 Sven Neuhaus <sven@sven.de>. All rights reserved.)
https://www.sven.de/fov/
:)