keep in mind that ppi (pixels per inch) is not the only deciding factor. what type of lcd panel is used will also affect image quality.
the larger resolution that you pack into a smaller physical space equates to a higher ppi. from just a quick google it seems that the average is around 85-100. my old 20.1 1600x1200 4:3 was about 100, the dell u3011 30 2560x1600 is about 84.
at normal distances to your monitor, you shouldnt notice the pixels at all. at minimum i would say you should be 18"-24" from the screen.
keep in mind that any pixelization could also be the source image you are looking at and not your monitor. lower quality images and digital video are prime examples of this. edges can sometimes appear jagged (called aliasing) as well which i suppose could be perceived as pixelization by some.
a good "average" screen size and resolution is a 20" or 22" 1920x1080 monitor.
as far as ppi goes, smartphones can double or triple typical monitor values. i know my android has 800px in resolution height and is only about 3.25" tall. thats about 250 ppi. though, on smartphones you typically are closer to them then a monitor so the additional ppi is needed.
just for your information, there was an ultra high ppi monitor created as a sort of test platform. it was a 20 inch 1:1 monitor with an effective resolution of 10,000x10,000. details could be seen with a magnifying glass. don't you just love technology?
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in general your ppi should be about average, though a step up wouldnt hurt things either. remember that panel type will affect perceived quality (especially on such things as gradients, viewing angles, color accuracy) and that your source image might be the culprit of pixelization.
if you can see the individual pixels from where you sit (if you can you must have good eyes!) then try sitting back farther.