iPhone Duo screen sizes, resolutions, and dimensions

iPhone Duo has two displays. Your app has to be comfortable on both, and it has to survive the moment someone opens or closes the phone. These are the numbers Apple publishes, and the ones the simulator reports. They are here so you can sketch. They are a bad thing to type into a layout.

The two displays

Apple says the two panels share an aspect ratio, so content scales in proportion as the device opens. The outer display has about 90 percent of the screen area of iPhone 18 Pro. The inner one is about 50 percent larger than iPhone 18 Pro Max.

In points

Layouts work in points, and Apple’s spec page lists pixels. The simulator’s device profile fills the gap. Blake Crosley read it from the iPhone Duo device type in Xcode 27.1 beta, and probe apps report the same windows:

Turn the phone and the numbers turn with it. Closed and held sideways, the outer display is compact in both width and height, a combination no tall phone ever showed you. Open and held upright, the inner display is 669 × 951 points and the fold runs across it as a horizontal band.

The outer panel is exactly three times its point size. The inner one is not: Apple lists 1878 × 2670 pixels, and the simulator draws 2007 × 2853. If the hardware matches the profile, the inner display shows a 3x render scaled down to fit, the way iPhone 6 Plus did. That is still an inference. It can be checked on the phone now, and we haven’t confirmed it. Either way, never do pixel math with a hardcoded scale. Read the scale of the screen you are on, with traitCollection.displayScale or the screen of your window scene.

The window is not the space you can use. Closed, Gautham Vijayan’s library reads safe-area insets of 84 points on the right and 34 at the bottom: the vertical bar takes one side. Open, Blake’s probe had 867 × 553 points of content inside the 951 × 669 window, with the bars down the trailing edge. Every pose’s insets, occlusions and crease, in window coordinates, are in the measurements from adapting Flicit. Treat these as a picture of one simulator build, not a constant.

It opens sideways

The chassis tells you how people will hold it:

It weighs 254 grams. The height stays put. The width almost doubles. Held the natural way, the inner display is a landscape canvas: an open paperback, not a tall phone. Apple lists the resolution portrait-first, the way it does for iPad, and the simulator agrees the open window is 951 points wide. The pose most people will see is wide. Apps that use the width put more side by side: Tripsy puts its places list beside the map, and Timeboxd goes from two watches across to six.

Sketch the inner layouts as landscape artboards first. Weng Tianxin, designing Camarts 3.0, gave that width to the photos, which are mostly landscape, rather than to a side column. The design guide has that layout and when it is the right call.

The hardware fold is not a column gap you can compute from these millimeters. The system reports the crease as its own region, 40 points wide in the simulator, and that region only becomes an active layout input while the phone is partly folded. See the fold guide.

What changes with the SDK

An app built with an older SDK still runs. It does not suddenly become a Duo app.

Apple’s engineers, in the September group lab Anton Gubarenko wrote up, described three steps. An app built with Xcode 26 is letterboxed: an iPhone-shaped panel on the outer display, and that same panel centered on the inner display. It does not react to the seated pose. Linking against iOS 27 turns resizability on, and you cannot turn it back off to “wait until the layout is ready.” Xcode 27.1 is the SDK that reaches the screen edge and moves standard bar buttons onto the side.

Blake Crosley measured the middle step. Linked against iOS 27.0, a probe got a 386-point window on the 466-point outer display, beside a black rail, with horizontal bars and no reserved regions. Linked against 27.1, the same code got the whole display. The checklist has the practical version, including how to check which SDK your binary was really linked against.

Don’t hardcode any of this

Apple’s wording is direct: avoid fixed widths, breakpoints, and any metric tied to a specific screen. A .frame(width:) copied from a current iPhone, a UIScreen.main helper in a constants file, and a layout that checks userInterfaceIdiom == .pad all miss Duo in a different way. UIScreen.main is the sharpest of the three: Blake found it still reports the 466 × 678 outer display while the app is running on the inner one.

Wang Shudao hit the practical version while getting a clock app ready for launch. Themes laid out with SwiftUI mostly fit, because they were already adaptive. Themes built on UIScreen and magic numbers did not. Wang pointed to fatbobman’s piece on size class and available space, and that is the right model: horizontalSizeClass says which system presentation fits the environment. It is not a measurement of the window. The geometry of the view is.

Two consequences fall out of the panels above:

• The outer display is compact width. The inner display is regular width and regular height.
• Apple says Duo respects your supported orientations, but the app still scales to fill the inner display. Rotate it in the simulator even when the app is portrait-locked.

Safe areas are frequently uneven, so the left inset is not a substitute for the right inset. A worked example and the test are in the checklist.

The rest of the spec sheet

The numbers above are the ones that shape a layout. These are the rest, from Apple’s announcement, for anyone deciding whether to buy one or writing copy about it.

Two of those matter to code. Touch ID means a prompt that says “Face ID” is wrong on this phone, so read LAContext.biometryType instead of typing the name. And the Dynamic Island sits vertically at the side of both displays, which is part of why the status area is a reserved region rather than a strip across the top.