Per-App Text Size Scaling in iOS 15 Explained

Apple's iOS 15 introduced the ability to adjust system text size on a per-app basis, moving away from the previous all-or-nothing approach to Dynamic Type. This feature allows users to set independent font scaling for individual applications without altering the typography across the rest of the operating system. The following overview details how this per-app scaling functions, how to configure it, and its technical limitations.

How Per-App Text Scaling Functions

Per-app text size adjustments are managed dynamically through the iOS Control Center rather than the standard Settings menu.

When you trigger the Text Size control inside an active application, the interface presents a segmented toggle at the bottom of the screen with two choices:

  • [App Name] Only
  • All Apps

Selecting [App Name] Only applies the chosen slider percentage strictly to the foreground application. The operating system creates an isolated preference entry for that specific bundle ID. This setting is persistent: closing the app, removing it from the app switcher, or restarting the device retains the chosen scale.

Interaction with Dynamic Type

The feature relies entirely on Apple’s Dynamic Type API.

  • Supported Apps: When an app supports Dynamic Type, adjusting the slider scales fonts, reconfigures line heights, and adapts responsive UI elements (such as table rows and navigation bars) to maintain legibility.
  • Unsupported Apps: Apps that use hardcoded font sizes, fixed-height containers, or custom non-native rendering engines (such as certain games or web wrappers) will ignore these scaling requests or experience visual clipping.

Hierarchy and Accessibility Sizes

Per-app scaling sits directly on top of the global system font settings:

  1. System Default as the Baseline: If an app is set to "All Apps," it mirrors whatever universal scale is configured in Settings > Display & Brightness > Text Size.
  2. Local Overrides: Changing the slider to "[App Name] Only" breaks the app away from the global tier. Future universal changes to "All Apps" will not alter the customized app unless it is manually re-synced.
  3. Larger Accessibility Sizes: If Larger Accessibility Sizes is enabled under Settings > Accessibility > Display & Text Size, the per-app Control Center slider expands from the standard 7-tier scale to the 12-tier accessibility scale, allowing extreme magnification in target apps without cluttering less text-heavy apps.

Resetting App-Specific Text Scaling

To revert an app to the system baseline, open the target application, swipe down to reveal the Control Center, tap the Text Size icon, and either set the slider to match the default percentage or switch the bottom selector back to All Apps.