# Mobile displays: understanding the inches Posted by The difference between several screen sizes of mobile devices have always been a wonder to me. I use a 5.3 inch device and when compared with a 7 inch device, it still looks small. Here is an excerpt from a Quezi question explaining how screen size is measured:

The size of a mobile phone display or of a computer monitor is given by a single length in millimeters, centimeters or inches. This measurement is taken diagonally, so it gives the largest straight-line measurement that can be obtained from the display. The quoted screen size, being a diagonal, is larger than the height or the width of the display.

Read more about how screen size and aspect ratios are measured on the Quezi question page.

I get the fact that screen sizes are measured diagonally but what I cannot seem to get is how astronomically different a 7 inch device is from a 10 inch device for example. Afterall, two Samsung Galaxy Notes do not make a Galaxy Tab 10.1 (in size that is).

Perhaps you can weigh in your views on differences between screen sizes.

1. eye_bee_kay says:

To calculate the area of a screen (oblong/square) – with a diagonal z inches, get the sides (x,y), then multiply the sides.

If we assume an aspect rational of 16:9, we have the following simultaneous equations to solve:

x^2 + y^2 = z^2 (z is 3.2″ for my dear Nokia 5800)
y = (16/9)x (assuming 16:9 ratio of long_side to short_side

solve for x and y

2. Harry Echemco says:

A little grasp of mathematics would have given you all the clue you need. The simply, though somewhat technical explanation is that the jump or increase from 5.3″ to 7″ diagonal length is as a result of a simple arithmetic addition, that is 5.3 + 1.7 = 7, while the area which you compared physically results from a geometrical evaluation of the length and the width and is calculated by multiplying the length of the screen by the width.

To make things a little simpler, let’s assume the diagonal measurement of your phone is 5″ instead of 5.3″, and let’s assume an aspect ratio of 3:4 then, it means your device’s width is 3″, the length is 4″ while the quoted screen size is 5″ which is also the measured diagonal distance and the area is (length * width) 4 * 3 = 12 sq. inch.

I will omit the units from now on so that it does not complicate things.

Taking the diagonal distance up to 7 (the quoted screen size) while still maintaining the original aspect ratio of 3:4 implies arithmetic or rather simple addition of 2 to 5 to give 7. For the area, while still on this same aspect ratio, the width will increase by 1.2 to 4.2, while the length will increase by 1.6 to give 5.6, the area now becomes 4.2 * 5.6 = 23.52

So from this, you can see by increasing quoted screen size by just 2 units almost doubles the original area, that is from 12 units to 23.52 units, and as the screen size increases, every little increase in the quoted screen size (diagonal length always), produces even more pronounced increase in area. That’s mathematics for you and as you can see is very real.

3. eye_bee_kay says:

By the way, @Harry, ‘HandyCalc’ app for Android claims it can solve that simultaneous equation above.

But, somehow, I have not been able to get it to solve it…

4. Abimbola Sojimi says:

In a language we mere mortals can understand: if you double the diagonal screen size, you quadruple the screen area eg a 7inch screen device has 4times the screen area of a 3.5inch screen device not double.

5. glenda says:

Abimbola Sojimi:

You are the man! What is the fuzz with all this calculations? You explained it in one sentence my friend.

6. Abimbola Sojimi says:

Thanks Glenda.

7. Mr. Mo says:

Wait! Simultaneous equations? Hold on let me check what site I’m on……

8. efe says:

Abimbola’s comment was the panadol for the headache induced by Harry and eyebeekay.

9. Jenuwa says:

Ha! Thanks Abimbola….almost went bonkers!

10. Adesope Wasiu says:

@Harry,The 4.2 and 5.6 you brought will have to be obtained using the method proposed by EyeBeeKay.Thumbs up for you guys cos u reawakened my arithmetic skills

11. Harry Echemco says: