“I’ve spent much of the last month trying to figure out the pixel counts for these displays, and it’s actually quite tricky,” Gruber writes. “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, horizontally and vertical,” Gruber writes. “@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.”
How Gruber derived these figures and uch more in the full article – recommended – here.