What is PPI and how it’s calculated

+1 vote
I’m picking up a new mobile and can’t understand what is pixels density – PPI . How much it should be? As far as I understand, it’s a very important characteristic of a phone’s screen.
asked Nov 19, 2016 in Goods and services by anonymous

1 Answer

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What is PPI (pixels density)

PPI is an acronym for «pixels per inch». Of course, the more its value, the more is pixel density; at this the pixels themselves are less in size which as a result provides a more clear picture on the screen of smartphone (and on the screen of any other gadget – tablet, monitor, TV and so on). At small PPI values you can see separate pixels on the screen; the picture will be grainy, which is not very comfortable for eyes. As a rule the mobiles with small PPI values are very cheap models.

How to calculate PPI

To calculate the PPI of any screen yourself you need to know its width and height resolution, as well as the diagonal of the screen in inches. The formula of PPI calculation looks like this: you need to take the square root of sum of squared width and height pixels and then divide the result by the screen diagonal in inches. That is the formula will look like this: 

How to calculate PPI

Let’s make the calculations with iPhone 7 as an example. It’s resolution is 1334 by 750 pixels, and it’s diagonal is 4.7 inches, that is:

Squared 1334 = 1779556;
Squared 750 = 562500;
The sum, 1779556 + 562500 = 2342056;
Take the square root of 2342056 = 1530.378;
Divide the result by 4.7 = 325.6123;
Round it downward 326. That is the PPI for iPhone 7.

What should be a phone PPI

There is no need to strive for the biggest values of PPI. Modern market offers the models with PPI more than 400 and even more than 500. But the problem is that human’s eye fails to notice the difference at PPI more than 300. Of course, if there is a special wish, you can see the pixels at very close distance, but with an ordinary use of the phone on the distance of 20-25 cm from your eyes, the screen will be quite comfortable. At this, high resolution processing influences the working time of your phone.

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answered Nov 19, 2016 by Expert Ryan (8,620 points)
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