iPhone Duo Screen Size: Inner vs Outer Display Specs

Quick answer: When the iPhone Duo is closed, you use the 6.3-inch cover display at 1206 × 2622 (19.5:9). When you open it, the 7.6-inch inner display takes over at 2670 × 1878, 430 PPI, and a 10:7 aspect ratio with 120Hz ProMotion. Same phone, two different shapes. Your apps and websites need to handle both.

If you only remember one diagonal, you will mis-size layouts. Book-style foldables are built around that gap. This guide pulls numbers from our device database and lines them up next to slab iPhones and other foldables so you can compare without digging through spec PDFs.

What is the iPhone Duo screen size?

Apple quotes screen size as a diagonal across the active display area. The iPhone Duo is a book-style foldable, so Apple (and our database) list two diagonals:

Display	When you use it	Diagonal	Resolution	Aspect ratio	PPI
Cover (outer)	Phone folded shut	6.3″	1206 × 2622	19.5:9	~460 PPI
Inner (main)	Phone unfolded	7.6″	2670 × 1878	10:7	430 PPI

The inner panel is a Super Retina XDR OLED Foldable with up to 3000 nits peak outdoor brightness and 120Hz ProMotion. The cover behaves like a tall phone screen. The inner panel is wider and squarer, closer to a small tablet than a standard iPhone.

Full specs live on the iPhone Duo device page. For every foldable we track, see the foldable screen size comparison hub.

Cover display vs inner display: what changes in practice

Cover (outer) display. At 6.3 inches and 19.5:9, the closed experience is in the same ballpark as a mainstream iPhone height-wise. You get one-handed reach, narrow CSS widths, and phone-style scrolling. Notifications, quick replies, and camera framing usually stay on this screen.

Inner display. At 7.6 inches and 10:7, width jumps. Reading, split view, and landscape video use the extra horizontal space. The diagonal is only modestly larger than the cover number suggests, but aspect ratio changes total area. A 7.6″ inner panel is not the same canvas as a 7.6″ tall phone would be.

Our database also lists unfolded active area at roughly 6.48 × 4.64 inches (164.6 × 117.8 mm) for the inner panel. Folded body size is about 73.5 × 160.9 mm with ~8.9 mm thickness. Unfolded width is about 143.5 mm across the hinge.

How the iPhone Duo compares to slab iPhones

The cover display lines up with the current 6.3-inch iPhone generation:

Model	Screen size	Resolution	PPI
iPhone 17	6.3″	2778 × 1284	460 PPI
iPhone 17 Pro	6.3″	2778 × 1284	460 PPI
iPhone Duo (cover)	6.3″	1206 × 2622	~460 PPI
iPhone Duo (inner)	7.6″	2670 × 1878	430 PPI

The cover is the size you already design for if you target modern iPhones. The inner is a second breakpoint. If you only test on a 6.3″ slab, you will not see layout bugs that show up on the wide inner panel.

Compare at a glance: iPhone Duo vs iPhone 17, or iPhone Duo vs Galaxy Z Fold8 for another book-style foldable.

Inner vs outer: resolution and pixel density

Resolution and PPI are not identical across the two panels:

• Cover: 1206 × 2622 pixels on a 6.3″ diagonal (~460 PPI class density).
• Inner: 2670 × 1878 pixels on a 7.6″ diagonal at 430 PPI (listed in our database).

Higher PPI on the cover is typical for foldables: the outer screen is smaller, so pixels pack tighter. The inner trades a slightly lower PPI for a much wider layout. For UI design, both are sharp enough that bitmap assets should still be served at 2× or 3× where iOS expects them.

Run your own numbers with the PPI calculator or read pixel density vs resolution if you want the math behind the labels.

Physical size, aspect ratio, and video

Diagonal inches hide shape. The cover is 19.5:9 (phone-tall). The inner is 10:7 (noticeably squarer).

That matters for 16:9 video. On a tall phone, video often fills most of the width. On a squarer inner panel, you may see more letterboxing even though the diagonal grew. Maps, documents, and two-column apps benefit more from the inner aspect ratio than fullscreen YouTube does.

See how diagonals can mislead across form factors in our foldable comparison table and aspect ratio guide.

CSS viewport and responsive layout on iPhone Duo

We treat CSS viewport width as a separate question from marketing resolution. System scaling, Safari chrome, and which display is active (cover vs inner) all change window.innerWidth.

Do not assume one viewport per device slug. Foldables need at least:

1. A narrow layout for the cover (~phone-width breakpoints).
2. A wide layout for the inner (~tablet-width breakpoints).

Approximate portrait CSS widths are useful for planning, but they are not a substitute for measuring on hardware. Use the viewport checker on a real iPhone Duo in both folded and unfolded states. Pair that with the breakpoint checker and viewport vs screen width vs DPR.

For Android foldable viewport patterns (same conceptual problem, different numbers), see Android CSS viewport sizes.

How to check iPhone Duo screen size yourself

1. Closed: note cover behavior in Settings → Display, then open the screen resolution checker in Safari on the cover.
2. Open: repeat on the inner panel. Resolution should report the inner pixel grid (2670 × 1878 class).
3. Layout width: use the viewport checker for CSS pixels your stylesheet sees.
4. DPR: confirm scaling with the device pixel ratio checker.

For inch measurements, Apple’s tech specs list each display, or measure corner to corner across the lit area only.

FAQ

What size is the iPhone Duo inner screen?

The inner display is 7.6 inches diagonally at 2670 × 1878 resolution, 430 PPI, and a 10:7 aspect ratio with 120Hz ProMotion.

What size is the iPhone Duo cover screen?

The cover (outer) display is 6.3 inches at 1206 × 2622 with a 19.5:9 aspect ratio, similar in height class to a 6.3-inch slab iPhone.

Does the iPhone Duo have two screen sizes?

Yes. Folded shut, you use the cover display. Unfolded, you use the inner display. Each has its own diagonal, resolution, and aspect ratio.

Is the iPhone Duo inner screen bigger than an iPhone 17 Pro Max?

The inner diagonal (7.6″) is larger than the iPhone 17 Pro Max (6.9″), but the inner aspect ratio is squarer. Total area and usable width differ from a tall 6.9″ phone. Compare both on the iPhone Duo vs 17 Pro Max page.

The short answer

The iPhone Duo is two devices in one chassis: a 6.3-inch cover for folded phone use and a 7.6-inch inner panel when open. Cover is tall (19.5:9); inner is wide (10:7). Resolution, PPI, and CSS viewport all shift between them.

Next steps: full iPhone Duo specs, compare all foldable screen sizes, or mobile screen sizes in 2026 for the wider phone landscape.