what are the size classes for the new iPhone X models?

Question

Apple has introduced three new iPhone X models: the iPhone XR, XS, and XS Max. What are their size classes, and how do these compare to other iPhone models?

Answer 1

I'll give three pieces of information for each model: the size classes when in portrait, the size classes when in landscape, and the screen resolution.

↔︎ means horizontal (width) size class
↕︎ means vertical (height) size class

The good old-fashioned standard is something like the iPhone 6s:

iPhone 6s: ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 2.0

The three models with Plus in their name, however, when in landscape, are regular, compact instead of compact, compact. In effect, an app that runs on these models finds its environment turning from an iPhone to something more like an iPad when the app rotates. They are also triple-resolution. For example:

iPhone 8 Plus: ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 3.0

Very well. How do the iPhone X models fit into this pattern?

iPhone X:      ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0
iPhone XR:     ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 2.0
iPhone XS:     ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0
iPhone XS Max: ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 3.0

So, the XR and the XS Max are like the Plus models as far as size classes are concerned. The XR is the odd man out in that it is only double-resolution.

EDIT And now the iPhone 11 models:

iPhone 11:         ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 2.0
iPhone 11 Pro:     ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0
iPhone 11 Pro Max: ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 3.0

So the iPhone 11 and the iPhone 11 Pro Max are both "big" in the same way as the Plus models.

EDIT 2 and 3 And the iPhone 12 and 13 models:

iPhone 12/13:         ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0
iPhone 12/13 Pro:     ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0
iPhone 12/13 Pro Max: ↔︎ compact, ↕︎ regular; ↔︎ regular, ↕︎ compact; 3.0
iPhone 12/13 mini:    ↔︎ compact, ↕︎ regular; ↔︎ compact, ↕︎ compact; 3.0

So only the iPhone 12 and 13 Pro Max are "big" like the Plus models.

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Finally, for completeness, the iPads. They are all

iPad: ↔︎ regular, ↕︎ regular; ↔︎ regular, ↕︎ regular; 2.0

But of course with iPad multitasking, an iPad window can take on the size class characteristics of an iPhone.

There are no current single-resolution iPhones or iPads, and there are no triple-resolution iPads.