PPI: The final unknown parameter of a device’s screen quality

Almost everyone who buys a phone focuses on the amount of RAM, the number of built-in memory, the processor, camera and... screen resolution. Usually, when we want to gain some information about that final parameter, we come across the abbreviation PPI. But what does it mean and what is its use?

What is PPI?

PPI stands for Pixels Per Inch. This means that the PPI number tells us how many pixels will be “used” per inch of the display of a given device. Regardless of whether it is a smartphone, tablet, computer monitor or TV – each device with physical size and display will have a PPI value.

What does PPI tell us?

PPI tells us how “sharp” the image will be on a given device – the higher the number, the greater the sharpness.

How to calculate the PPI of the device?

To calculate a given device’s PPI:

1) We calculate the number of pixels diagonally of the device using the formula:

  • w – device width (in pixels)
  • h – device height (in pixels)

2) we divide the number of pixels by the physical (diagonal) size of the screen in inches:

  • dₒ – number of pixels in the diagonal of the device
  • dᵢ – device screen size

An example:
If our phone is a Samsung Galaxy S10
Device resolution according to the specifications is 1440 x 3040 pixels
The physical size of the screen according to the specifications is 6.1 inches:

If you don’t want to calculate PPI, you can use a calculator for this:

PPI Calculator (Pixels Per Inch)

What are the average PPI values ​​for specific devices?

What is standard PPI for specific device types? It is worth knowing to be able to compare your device with the “normal” market measurement. Selected values ​​are:

  • For modern smartphones: ~ 470 PPI
  • For modern tablets: ~ 225 PPI
  • For modern laptops: ~ 130 PPI (Full HD) / ~ 280 PPI (4K)
  • For modern monitors: ~ 90 PPI (Full HD) / ~ 163 PPI (4K)
  • For modern TVs: ~ 40 PPI (Full HD) / ~ 80 PPI (4K)

(Results calculated on the basis of an average of 5-6 devices of a given type from 2018/2019)

Is it worth looking for a device with the highest PPI?

Not quite – although PPI does suggest how “sharp” the image will be, human sight may not be able to fully process such a large number of small dots on the screen.

Let’s start with the fact that human vision has a number of flaws and does not work like a typical camera. It works more like a detective, collecting data from the environment and piecing it together to generate an image. Put simply, we don’t actually see as clearly as we think we do.

As an example, we can take the image shown above (How much PPI?). By approaching the screen you will probably be able to spot quality differences between 113 ppi and 376 ppi. What if you decide to move away from the screen? At some point, the difference will become invisible. Even with the awful 20 ppi there will be a moment when it will be difficult to notice the difference (although it is quite possible that you will have to look at the screen from the other end of the room).

It is also worth noting that the PPI parameter only tells us how sharp the image will be. What if it turns out to be too dark to make out at all? Then we can see nothing anyway.

Hence, there are a lot of factors that affect REAL (i.e. what we see) image quality. In addition, there are many variables that can affect it, such as simple eye fatigue.

A small piece of trivia

Telephones with the highest PPI were actually produced two and four years ago. Here they are:

Sony Xperia XZ Premium with a 4K screen, having the largest PPI of 807 pixels per inch.
Year of production 2017.

 

Sony Xperia Z5 Premium with a 4K screen, with the second-largest PPI – 801 pixels per inch.
Year of production 2015.

 

And what PPI value does a premium class phone made in 2019 have? For example:

Samsung Galaxy S10+  “only” 526 ppi
Huawei P30 Pro – “just” 398 ppi

If you find yourself in a store, feel free to compare the image they display with one of those flagship devices and assess the differences yourself,
(I assure you, those with the lower PPI amount will look smoother)

End of trivia.

The facts are as follows:

  • The human eye can only catch a certain amount of detail depending on the distance to the screen. The further we are from the object we look at, the less detail we see.
  • Image quality is strongly dependent on the lighting of the device. Not all types of screen lighting are equal.
    This is also the reason for the existence of many technologies such as OLED, QLED, AMOLED etc., which manipulate the light generated by devices in different ways so that the screens retain the best clarity.
  • The higher the PPI, the harder the device must work to show the image.

In this situation, the question remains: What is the magic PPI number, after which this value is no longer critical? This can also be calculated!

The resolution of the human eye

Using a certain formula, we can calculate the “resolution” optimal for a given display, assuming being at a certain distance from it.
Of course, human vision is very complicated and has a lot of variables that affect how we see something. In a nutshell:

  • Optimal PPI for a 6.1-inch smartphone at a distance of 25cm: ~340 PPI
  • Optimal PPI for a 10.1-inch tablet at a distance of 30cm: ~277 PPI
  • Optimal PPI for a 24-inch monitor at a distance of 50cm: ~159 PPI
  • Optimal PPI for a 55-inch TV at a distance of 140cm: ~58 PPI

When our device’s PPI has more than the given optimal value, the perception of better resolution will be negligible. Of course, it can all be “rearranged”, by, for example, changing the distance at which we are from a given device (if you have a Full HD TV, then approaching it centimeter by centimeter you will start to see the pixels separately – watch out for your eyes because they will start to hurt after a few seconds).

If you want to calculate the optimal PPI number for a specific device yourself, you can use this calculator

If you’re very curious about how to estimate optimal visual acuity, you can find more information here

How do you find the best quality screen?

In the case of screens, it is better not to go by the specification, but the more subjective feeling you get, especially when you are going to spend hours staring at them.

What is the point of amazing screen clarity, if after 5 minutes of looking at the screen we begin to get a headache?

Therefore, if we want to know if the quality of a given image is appropriate for us, there is no other way but to spend time with the device (going first to the electronics/household appliances store) and after using it for 15 minutes of doing the following:

  • Reading static text (white text, no movement);
  • Watching a film clip with different light intensities (night – dark colors, day – bright colors, etc.)
    (My recommendation for that would be watching the following YouTube recording “Sony 4K Demo: Another World”)

You should ask yourself the following questions:

  • Do I feel comfortable looking at an image on this device?
  • Is the quality of the display I’m looking at sufficient for me?

It is also worth remembering that modern devices have a multitude of settings that can affect the final quality of the image we see. So do not be afraid to experiment with device settings to find the optimal display for you (though before starting, check how to restore factory settings – just in case).

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