Working out the pixel density, or pixels-per-inch (ppi) of a device can give a good indication of how clear the screen of a smartphone can be and tech websites (like us) are throwing around the pixel density of devices like it’s going out of fashion.
Here, we go over what ppi means, how it's calculated and whether we should really care about it.
What does this mean?
The first thing to note when talking ppi is that it’s the pixel density, so if you have a large device like the Samsung Galaxy Mega 6.3, even if it has a super-high resolution, it will have a much lower ppi that the Samsung Galaxy S4, for example, because the pixels are spread across a much larger area.
Think of a phone screen as a grid, where the pixels line up in rows and columns. With the Samsung Galaxy Mega 6.3, there are 720 pixels across the screen and 1280 down the screen, if you're holding it in portrait mode. We refer to the Samsung Galaxy Mega 6.3 as having a resolution of 720x1280.
Just to complicate things, HD displays are measured in terms of the pixels going across the screen, so in the example of the Samsung Galaxy Mega 6.3 it is referred to as a 720p screen. A Full HD screen comprises 1080 pixels going across it, so the Sony Xperia Z Ultra is described as having a Full HD 1080p display.
How do you work out the ppi of a device?
In layman's terms, ppi refers to the number of pixels spread across the surface area of the screen, but because screens are measured diagonally it's not as straightforward as multiplying the pixel count going across the device by the number down and then dividing by the diagonal measurement.
For ease (and speed), we use a ready-made ppi calculator that allows you to find out the ppi of any screen without getting involved in Pythagoras Theorem.
The thing with ppi is that the larger the screen, the lower the ppi. This is because a larger screen means the individual pixels have to be larger to fill the space.
Both the Samsung Galaxy Mega 6.3 and the Samsung Galaxy S3 have different sized screens, but as they each have 720x1280 pixels they also have the same number of pixels in that screen.
At 6.3-inches, the Galaxy Mega 6.3 has a ppi of around 233, but the Samsung Galaxy S3's ppi is 305 because although it has the same number of pixels, they are concentrated into a smaller area - a 4.8-inch display - and can therefore use smaller pixels.
But does ppi matter?
The interesting thing about devices that boast a higher ppi that 400 is that your eyes can't see the high concentration of pixels at normal smartphone viewing distances. Your naked eye can only see densities of up to 399, so you won't be able to tell the difference between a device with a ppi of 400 and 440 (the Samsung Galaxy S4, for example).
In conclusion, what we call 'Full HD' screens only matter if you have a device that is 5.7-inches or bigger, when the pixels become bigger and therefore more visible.
by clareh via Featured Articles
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