react / react/react-native

maxFontSizeMultiplier works differently between iOS and Android

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#56,578 1 comment 12 reactions 0 assignees View on GitHub

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Needs: Triage :mag: Platform: Android Platform: iOS
Dominant language
C++
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Forks
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Avg merge
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Merged PRs (30d)
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Description

Description
  • maxFontSizeMultiplier affects the fontSize on both Android and iOS.
  • When font scaling is set to a value higher than maxFontSizeMultiplier, both Android and iOS clamp the fontSize value
  • When it comes to lineHeight, it acts differently. iOS clamps the value while Android ignores the maxFontSizeMultiplier for lineHeight

Please see the screenshots for a side-by-side comparison

Steps to reproduce
  1. Install he reproducer app with yarn android and yarn ios
  2. Take a screenshot of the app so you can compare later
  3. Increase the font scaling. You can either use the settings app, or cmd option + on iOS simulator, and adb shell settings put system font_scale <value> on Android
  4. Take another screenshot and compare those two
React Native Version

0.85.2

Affected Platforms

Runtime - iOS, Runtime - Android

Output of npx @react-native-community/cli info
info Fetching system and libraries information...
System:
  OS: macOS 15.7.4
  CPU: (12) arm64 Apple M4 Pro
  Memory: 258.47 MB / 48.00 GB
  Shell:
    version: 0.109.1
    path: /Users/burakguner/.cargo/bin/nu
Binaries:
  Node:
    version: 24.13.0
    path: /Users/burakguner/.nix-profile/bin/node
  Yarn:
    version: 1.22.22
    path: /Users/burakguner/.nix-profile/bin/yarn
  npm:
    version: 11.6.2
    path: /Users/burakguner/.nix-profile/bin/npm
  Watchman:
    version: 2026.01.19.00
    path: /Users/burakguner/.nix-profile/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/burakguner/.local/share/gem/ruby/3.3.0/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.2
      - iOS 26.2
      - macOS 26.2
      - tvOS 26.2
      - visionOS 26.2
      - watchOS 26.2
  Android SDK:
    API Levels:
      - "30"
      - "31"
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 35.0.0
      - 36.0.0
      - 36.1.0
    System Images:
      - android-30 | ARM 64 v8a
      - android-34 | Google Play ARM 64 v8a
      - android-35 | Google APIs ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
      - android-36.1 | Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2025.3 AI-253.32098.37.2534.15232325
  Xcode:
    version: 26.2/17C52
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 21.0.8
    path: /Users/burakguner/.nix-profile/bin/javac
  Ruby:
    version: 3.4.8
    path: /Users/burakguner/.nix-profile/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.85.2
    wanted: 0.85.2
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true
Stacktrace or Logs
N/A
MANDATORY Reproducer

https://github.com/atlj/reproducer-max-font-size-multiplier-line-height

Screenshots and Videos
Font Scale iOS Android
1 Image Image
2.143 Image Image

Notice how lineHeight is not clamped on Android screenshots

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the mandatory reproducer app and run it with yarn android and yarn ios. Compare screenshots at normal and increased font scales using the issue's settings commands; done means Android lineHeight is clamped by maxFontSizeMultiplier consistently with iOS.

Written by the indexing model from the issue text.

Assessment

Tech stack
android, ios, react-native
Domain
mobile
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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