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A paper notebook was the starting point for the first foldable iPhone – Apple's designers reveal this in a new interview. The proportions are said to be based on the international A-size paper format, which is known to everyone in Germany as DIN A4. A comparison with Apple's own measurements shows just how close the device actually is to this standard.
Apple CEO John Ternus, Molly Anderson, Vice President of Industrial Design, and Steve Lemay, Vice President of Human Interface Design, spoke with British GQ about the development of the iPhone Duo. The interview with GQ covers both hardware and software. Pre-orders begin on October 16th, and the device will be available in stores from October 23rd, starting at €2,299 in Germany.
Key Facts at a Glance
- According to Anderson, an ordinary paper notebook was a key inspiration for the iPhone Duo.
- According to GQ, the proportions are based on the A-size paper format, so the device has the same aspect ratio whether open or closed.
- Apple's official measurements confirm this: Both states are around 1.40 to 1, only about one percent below the DIN ratio.
- Theoretically, an A4 page fills the internal display to within 14 pixels.
- The software is designed to combine experiences from iPad, Mac and iPhone without feeling like a different system when opened.
The notebook as a starting point
Ternus connects the device to a well-known phrase used by his predecessor. Steve Jobs spoke of the connection between technology and the humanities, and the iPhone Duo is a perfect example of this. Jobs had used this formula, among other times, when introducing the iPad 2 in 2011.
Anderson elaborates. Everyone knows how a notebook feels in a pocket and how it's carried. The guiding question was how a device could offer a large surface area while still feeling compact.
According to Anderson, a great deal of attention was paid to the opening mechanism. The hinge follows a specially calibrated, variable torque curve: It opens easily and is then designed to stay open on its own and lie flat.
Proportions according to the DIN principle
According to GQ, the proportions of the iPhone Duo are derived from the A-size paper format. Its core aspect ratio is 1 to the square root of 2, or approximately 1 to 1.414. If you halve such a sheet, the ratio remains the same – A4 becomes A5, A5 becomes A6. This is precisely the property required for a device that is intended to have the same shape whether open or closed.
The system has German origins. The German Institute for Standardization published the standard DIN 476 on August 18, 1922, developed by the engineer Walter Porstmann. Today it is internationally standardized as ISO 216, but in German-speaking countries it is still referred to as DIN A4.
The iPhone Duo's technical specifications allow for this calculation. When open, the device measures 164.6 by 117.8 millimeters; when closed, it measures 117.8 by 84.1 millimeters.
| Format | Dimensions (mm) | Aspect ratio |
|---|---|---|
| DIN A5 | 210 × 148 | 1,414 |
| iPhone Duo opened | 164,6 × 117,8 | 1,397 |
| DIN A6 | 148 × 105 | 1,414 |
| iPhone Duo closed | 117,8 × 84,1 | 1,401 |
| DIN A7 | 105 × 74 | 1,414 |
Both states are only about one percent below the DIN standard and almost identical in size. When unfolded, the iPhone Duo is larger than an A6 postcard and smaller than an A5 notebook; when folded, it measures between A7 and A6.
Software from three worlds
Lemay describes the software as a culmination of previous experience. Users will find many features from the iPad, even the Mac and previous iPhones – a kind of "best of" these products.
It was important to the team that opening the device didn't feel like switching to a different operating system. Controls retain their positions so that no one has to search for the button they just saw after opening it. Apple had already demonstrated how iOS 27 adapts its interface when opening the device during its initial presentation.
Lemay also expects developers to find applications that the design team hadn't anticipated. Some of these could shape the device itself and the entire industry.
What the A-format brings to everyday life
For users in German-speaking countries, the choice of format has a tangible side effect. Invoices, forms, official letters, and most PDFs are in A4 format here. The internal display has a resolution of 1,878 by 2,670 pixels. A full-width A4 page would theoretically be 2,656 pixels high, thus filling the display to within 14 pixels.
In the US, the Letter format is common, which, at 8.5 by 11 inches, is more compact. A Letter page of the same width would only occupy about 91 percent of the display height. These figures are purely geometric – rounded corners and the controls of the respective app will, in practice, reduce the usable screen space.
If you work a lot with documents, this gives you an internal display that is precisely tailored to the page format in which almost all paper is available in this country.
Would you primarily use the unfolded iPhone Duo for reading documents – or is a foldable phone still just a smartphone with a bit more screen space for videos and apps? Let us know in the comments what you would use the A-frame side for.
