The iPhone X has a 458.67 PPI 5.85” screen with a resolution of 2436×1125 px, which translates to 812×375 pt @3x¹. These 375 pt are identical to what the 4.7” iPhone is capable of displaying (667×375 pt).

The 5.5” iPhones have a physical resolution of 1920×1080 px, but actually render the content in 2208×1242 px before downscaling it to fit the screen. This translates to 736×414 pt @3x.

If the rumoured iPhone X Plus retains the 458.67 PPI pixel density, it should get a 6.68” screen which would fit 2800×1242 px. This would be the equivalent of 933×414 pt, which lines up perfectly with the 5.5” models.

P.S. If we get an iPhone X SE (or SE X) with a similarity specced screen, it would have a resolution of 2078×960 px and a diagonal of 4.99”. Apple could choose to go down the @2x route, which would result in 1386×640 px.