In my previous post (2 Reasons Why the iPhone 6 Won’t Need to be 1.5x Retina Resolution), I explained why Apple isn’t so constrained about the rumored iPhone 6 screen sizes. That blog post was long enough, so I thought I’d break out into a new post exactly what size(s) I’m expecting in the iPhone 6 4.7″ and 5.5″ phones (assuming the rumors are real).

I’m thinking Apple will make both phones at 1920×1080. Then they will be able to contain letter-boxed 1.5x-sized existing apps (fitting inside a 1704×960 rectangle). Each phone will have 1.5x-sized tap targets (66 points tall instead of 44 points tall) but will still have an extra 10% or so extra space vertically (1920 vs 1704) and horizontally (1080 vs 960), so there’s a little more room for app content.

The benefit to users:

2 new phone sizes, each with a little more space for (updated) apps. One phone that has a larger screen so guys with big fingers have even larger tap targets (or anyone who wants to watch movies or browse the web on a “big screen”). By having the same resolution, things will be in the exact same relative position on the two devices; one will simply be larger (like the difference between a 42” and a 55” HDTV or the difference between the iPad Air and iPad mini). The larger tap target means it will be easier to hit a button without having to have great precision in finger movements.

The benefit to developers/UX/enterprises: Only one new pixel dimension to target (much as the iPad and iPad mini have the same pixel dimensions). Retina + 1.5x graphics that should work seamlessly (a new image naming convention of @3x?). Screens that only offer 10% or so extra space within apps mean that developers don’t have to spend a lot of time updating app content. And Auto Layout means that they probably don’t have to do anything other than recompile for them to work on the new iPhones.

Benefit to Apple: Only one set of pixel dimensions to order (1920×1080, although at 4.7” and 5.5” sizes). A presumably-cheaper industry standard screen dimension (full HD). No scaling of videos (which are mostly full HD nowadays).

Of course, just because this is logical doesn’t mean it’s going to happen. Maybe the 4.7” model will be exactly 1.5x larger (1704×960) and the 5.5” model will be full HD (1920×1280). Or maybe the 4.7″ model will be 1280×720 and the 5.5″ model will be 1920×1280. Apple always surprises me, and there may be marketing or other reasons to go down this path. But I’m definitely leaning toward the both-phones-are-full-HD scenario.