# Remove hard-coded screen dimensions and fixed frame widths

> Layout code that assumes a fixed iPhone width breaks immediately on the iPhone Duo inner display, which is 626 points wide instead of roughly 400.

Source: https://iphoneduosupport.com/checklist/hardcoded-screen-dimensions/

Severity: blocker
Category: layout
Applies to: all
Symptom: Content is stuck in a narrow column on the left, stretched past the edges, or overlapping after the device is unfolded.
Sources: https://developer.apple.com/videos/play/tech-talks/111461/ https://developer.apple.com/videos/play/tech-talks/111466/
Last verified: 2026-09-09

---

This is the single most common cause of broken layout on iPhone Duo, and it is worth auditing before anything else on this list.

## Why it happens

Every iPhone before iPhone Duo was between roughly 320 and 440 points wide. That made a hard-coded width look safe for years. The inner display is **626 × 890 points**, so any constant tuned for a 402-point iPhone 18 Pro is now off by more than 200 points.

Worse, the width now *changes at runtime*. The device folds, unfolds, rotates, and enters Split View multitasking, and your app moves between two physically different displays. A width captured once at launch is wrong within seconds of the user opening the device.

## Find it

Search your project for the patterns that bake in a width:

```bash
grep -rn "UIScreen.main.bounds" --include="*.swift" .
grep -rn "\.frame(width:" --include="*.swift" .
grep -rn "widthAnchor.constraint(equalToConstant:" --include="*.swift" .
```

Not every hit is a bug. A 44-point button is fine. What matters is anything sized as a proportion of, or a stand-in for, the screen.

## The fix

Let the layout system supply the size rather than asserting it.

```swift
// Before — a constant that was only ever right on one device class
content.frame(width: 390)

// After — fill the space you are given, with a readable upper bound
content
    .frame(maxWidth: .infinity)
    .frame(maxWidth: 700)   // cap line length, don't pin to a device
```

In UIKit, prefer relative constraints over constants:

```swift
// Before
view.widthAnchor.constraint(equalToConstant: 390).isActive = true

// After
NSLayoutConstraint.activate([
    content.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor),
    content.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor),
    content.widthAnchor.constraint(lessThanOrEqualToConstant: 700),
])
```

When you genuinely need the current size, read it reactively so it updates as the device folds:

```swift
GeometryReader { proxy in
    GalleryView(columns: proxy.size.width > 600 ? 3 : 1)
}
```

Apple's framing is to design across a **continuum of sizes** rather than for a set of known devices. A layout built that way needs no changes when the next form factor ships.

## How to verify

Run in the iPhone Duo simulator via Device Hub in Xcode 27.1 and use the on-screen controls to open, close, fold, and rotate while watching the layout. Anything that jumps, clips, or leaves a large empty band is a hard-coded value you have not found yet.

---

Published by iPhone Duo Support (https://iphoneduosupport.com). Not affiliated with Apple Inc.