It turns out that you need to be exactly three feet from a 1920x1080 24" monitor to experience the Retina effect of the iPhone 4. Not bad for a common monitor that can be had for less than $200, eh?

More combinations of screen size, viewing distance and the subsequent required rows of square pixels can be found here. Remember 1080p has 1080 rows of pixels, 1440p has 1440 rows and 4K (quad 1080p) has 2160 rows. The chart is only accurate for 16:9 resolutions.

Would someone mind checking my work? My results seem too good to be true.

ImSpartacus wrote:I used this new iPad slide and slightly modified formulas from this wikipedia page to find what resolution would yield Retina-i-ness on a screen of any size and aspect ratio.

Long story short,

sqrt(D^2H^2/(W^2+H^2))/2(d)tan(a/2)

is the height (short side) of this resolution and the width (long side) of the resolution can be found by multiplying the width and the aspect ratio. Variable definitions can be found at the two sources.

For a 24" 16:9 monitor viewed at 30" that has as much Retina-i-ness as the iPhone 4, we only need 1292.91 rows of pixels. So today's $200 1080p monitors are almost there. 1440p in a 24" 16:9 at 30" would be more Retina-y than the iPhone 4!

From a different perspective, a 24" 1080p monitor has as much Retina-i-ness as the iPhone 4 from 36" away (actually, you only need 1077 pixels at 36", so 1080 does the job).

So you'll be pleased to hear that you already have a retina display on your desk. Just get three feet away from it.