How do you count pixles are there like 100 pixles in a square inch??????
Oh this is deeep.... pixels per inch is totally dependant on the resolution
the user is using in Control Panel -> Display Properties -> Settings
There is an API function GetSystemMetrics that might be able to tell you. I
also remember hearing of something like TwipsPerPixel. a Twip is 1/1440 of
an inch, so if you know twips per pixel, you're one expression away from
pixels per inch.