Let's talk about diagonal screen measurements (the bright magenta line) and why a small increase is really a big increase. In this case we really need a picture to save 1000 words of description, so here you go:
The first screen above at the left is the 3.5-inch screen of an iPhone. The second image is a (never-to-be-built-by-Apple) 7-inch tablet, and the third image shows the 9.7-inch iPad. The diagonal measures are shown below the images on the screens.
The 7-inch screen's diagonal measure is only 72% of the largest screen - meaning it's 28% smaller (100-72=28). It's just about 3/4 the size.
The iPhone's diagonal measure is only 36% of the largest screen - a bit more than 1/3 the size.
This bright picture shows you a comparison of the surface area on these three screens. Did you notice the yellow rectangles in the first image? I took those and duplicated them on this picture.
The smallest one is 13% of surface area of the largest one. The yellow tint on that small screen is 13% of the intensity of the largest screen (almost looks white, doesn't it?). It's only 1/7th the size of the large one.
The rectangle in the middle represents the area of our 7-inch screen, which is 54% of the surface area of the large screen and for good measure, it's 54% of the intensity of yellow. It's just over 1/2 the size of the large one! (Just like Steve said ... )
So the large screen's surface area is 100%, the intermediate one 54%, and the smallest 13%, while the diagonal measures are 100%, 72% and 36%? Are you thinking, How can that be?
Let me just say, If you are confused by how that same 7-inch middle screen can be 72% when measured diagonally, and 54% when measured by area, welcome to elementary school math!