Want to know the resolution of the new iPhones due to be announced next month? John Gruber did the math — all of the math — to come up with the best educated guess I’ve seen:

But after giving it much thought, and a lot of tinkering in a spreadsheet, here is what I think Apple is going to do:

4.7-inch display: 1334 × 750, 326 PPI @2x
5.5-inch display: 2208 × 1242, 461 PPI @3x

@2x means the same “double” retina resolution that we’ve seen on all iOS devices with retina displays to date, where each virtual point in the user interface is represented by two physical pixels on the display in each dimension, horizontal and vertical. @3x means a new “triple” retina resolution, where each user interface point is represented by three display pixels. A single @2x point is a 2 × 2 square of 4 pixels; an @3x point is a 3 × 3 square of 9 pixels.

I could be wrong on either or both of these conjectured new iPhones. I derived these figures on my own, and I’ll explain my thought process below.

It’s a fascinating and extremely detailed (Ha! Get it?) report, explaining the difference between pixels and points on an iOS screen, and how simply increasing the pixels wouldn’t necessarily lead to fitting more stuff onto a larger screen — at least not in a sensible way, and not at resolutions other than the ones he determined.