iphone 5 screen size and converting points to inches

literature says the screen size is 568 x 320 points
i assume this because of the compactness of the retina display points and the typical conversion of 1/96 pixel = 1" does not apply

if i convert points to inches 1/72" = 1 point

568 x 320 points
7.888 x 4.444 inches

thats obviously not right what am I doing wrong?

need to know the absolute screen size (mm, cm, inches, etc) so I can draw a rectangle in photoshop respresenting the actual screen size.
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GaryConnect With a Mentor Commented:
Screen size = 1136 x 640 px
Pixels per inch = 326

1136/326 = 3.4846625 inches
640/326 = 1.963190 inches
glenn_rAuthor Commented:
then how do they get 568 x 320 points
How does who get? The screen resolution is 1136 x 640 px.
Maybe some confusion between what is a retina display
The higher resolution will be used when for example an image is displayed - you would have two copies of an image, one for normal displays and another that is twice the dimensions for retina displays.  On a retina device both images would be the same dimension but the retina version will have a lot more detail due to the doubling of the pixels.
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glenn_rAuthor Commented:
most illustrations show the size of the iphone 5 display at 568 x 320 points
that where i went wrong
if you convert those points to inches i produces different numbers they you gave above
any ideas on how they converted those points to inches?
If you want to use those dimensions then you need to halve the ppi - 326px becomes 163px
glenn_rAuthor Commented:
Not sure if I follow you on that one

ppi is 326 so what the calculation?
To the point.
The screen resolution is 1136 x 640 px - there is no if's and but's about it, that is what it is.
There are 326px per inch.

If you want to make your calculations based on a non retina display resolution then you halve everything including the ppi.
glenn_rAuthor Commented:
got the ppi explantion 100%

confused at why you halve everything for the point conversion
i understand that ppi is lxw and if so a square root of that number would produce the x & y size
can you articulate your work from a different angle?
I don't know how better to explain it.
On a retina display 1 pixel is actually 4 pixels - 2 across and 2 down

Take an image that is 1136 x 640 px (this would be how you would size an image for a retina display) - every pixel of the image uses 1 pixel on the display.

Take another image that is 568 x 320px - for every pixel of this image there are 4 pixels used.
This would also be the case for text and anything else that is not retina ready.
glenn_rAuthor Commented:
got it
keep thinking in terms of lxw or 2 px horizontal and 2 px vertical
make sense now
thanks for the explanations
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