There are a lot of Apple fans who are about to suddenly discover that their thumbs are actually longer than they previously thought, or have grown in the years since the first perfect iPhone was released.

The design of the iPhone is guided by what is technically possible as much as by ergonomics. As the size of our hands hasn't changed, how can a 4.7 inch phone now be perfect when previously 3.5 inch was deemed perfect? Here is one reason: as the devices become slimmer, your thumb can reach farther than before and hence cover a larger screen. So: it's the combination of thinness and size that makes the iPhone 6 still usable with one hand. I'm not denying that people might not care as much and simply want a bigger screen, too, and this is an additional factor.

> As the size of our hands hasn't changed, how can a 4.7 inch phone now be perfect when previously 3.5 inch was deemed perfect? Here is one reason: as the devices become slimmer, your thumb can reach farther than before and hence cover a larger screen.

Well, I'd say most of the problem here is trying to identify a two-dimensional screen by a single number, the length of its diagonal. It must make more sense to give the actual dimensions of screens.

I remember pained discussion of the Nexus 5 saying the 4 was wide enough. The 5 is only wider by a couple millimeters, but is significantly enough taller that they bumped the single number identifying its size. That's no way to communicate.

Doesn't perfect also depend on what you're trying to do?

It's all trade offs but as we increase what we do with our phones, a bigger screen potentially becomes more valuable.

I know a lot of people saying they have no interest in more than 3.5" or 4". Generally those people are fairly casual users. I also know "power users" (horrible term) who have been crying out for bigger screens.

I'm less worried about thumb size and more worried about how it feels in my pocket.