I Shrunk a Flutter Release From 68 MB to 27 MB With Every Feature Intact

I Shrunk a Flutter Release From 68 MB to 27 MB With Every Feature Intact

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A lab-style teardown you can copy this afternoon: exact flags, Gradle switches, asset diet, and what actually moved the needle

(Oct 22 2025) my release lit up a warning: "Larger than 80% of apps in your category."

No 4K videos. No ML models. Still 68 MB. Two nights later the same build — same features — shipped at 27 MB

Here's the notebook I wish I had on day one

The X-Ray: Where APK/IPA Size Really Comes From

  • Native libs per ABI (arm64-v8a, armeabi-v7a)
  • Dart AOT snapshot + debug symbols
  • Android resources / iOS slices
  • Fonts, icon fonts, images you listed in pubspec.yaml
  • Transitive deps dragging native code you don't use

If you don't measure each bucket, you'll argue taste instead of facts

① Ship the Right Artifact (Biggest Win)

Android

If you still push a single universal APK, you're gifting devices code they cannot execute.

flutter build apk --release --split-per-abi --target-platform=android-arm,android-arm64

Result on my build: 68 MB → 33 MB (nothing else changed)

Play-first? Use AAB

Dynamic Delivery sends only the device's ABI. Same codebase, smaller install for almost everyone:

flutter build appbundle --release

Rule: universal APK only for side-loading or private distribution. Otherwise AAB or per-ABI APKs

② Let R8 Throw Away What You Don't Use

Enable code shrinking + resource shrinking in your android/app/build.gradle:

android {
  buildTypes {
    release {
      minifyEnabled true           // R8 shrink & optimize bytecode
      shrinkResources true         // toss unused res
      proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'),
                    'proguard-rules.pro'
    }
  }
}

Keep rules (adjust package names):

# android/app/proguard-rules.pro
-keep class io.flutter.** { *; }
-keep class io.flutter.plugins.** { *; }
-keep class com.yourapp.** { *; }       # your entry points / DI singletons
-keep class *.MainActivity { *; }       # launcher activity

Net on my build: ~3–4 MB trimmed after ABI split

③ Strip Debug Info (But Keep It for Crashes)

Flutter can move symbol data out of the binary so users don't download it, while you keep files to de-obfuscate stack traces.

Android (APK/AAB) & iOS (IPA):

flutter build appbundle \
  --release \
  --obfuscate \
  --split-debug-info=build/symbols/2025-08-22
  • — obfuscate often trims a couple MB on medium apps
  • — split-debug-info writes symbol files to the directory you choose — commit or upload to your crash backend

On my build: ~2 MB saved and readable crashes preserved

④ Stop Shipping Every Icon Ever Made

Material icon fonts can be huge. Flutter can include only the glyphs you use:

flutter build apk --release --split-per-abi --tree-shake-icons

If you use many icons across feature flags, consider SVGs for one-offs via flutter_svg, or a subset font generated during CI

Savings vary, mine was ~1–2 MB

⑤ Asset Diet (The Boring Work That Pays)

In pubspec.yaml list exact files, not whole folders:

flutter:
  assets:
    - assets/images/logo.webp
    - assets/intro/slide_1.webp
    - assets/intro/slide_2.webp
  • Convert PNG→WebP (or AVIF if your viewer supports it). Keep a PNG fallback only when transparency or quality demands it
  • Delete test images, outdated Lotties, unused fonts
  • For Lottie, prefer optimized JSON and cache wisely

My sweep: 33 MB → 29 MB

Quick find:

# list everything Flutter will bundle
grep -R "assets:" -n pubspec.yaml

⑥ Dependency Audit (Transitives Are Sneaky)

Ask: "Does this plugin pull native code I never execute?"

  • Replace heavy analytics with a light logger if you don't need device-side SDKs
  • Remove video/ML packages used on a single, seldom-used screen
  • Consolidate HTTP stacks (don't ship both http and dio unless needed)

Tools:

flutter pub deps --style=compact
dart pub outdated

⑦ Load Later What Users Don't Need Now (Dart Deferred)

For big, rare features (editor, charts, map), defer their code until first use:

import 'package:pro/editor.dart' deferred as editor;

Future<void> openEditor() async {
  await editor.loadLibrary();
  Navigator.of(context).push(MaterialPageRoute(
    builder: (_) => editor.EditorScreen(),
  ));
}
  • Measurable binary reduction when the feature is sizeable
  • Cold start feels snappier; first open of that feature pays the cost once

⑧ iOS Notes That Actually Help

  • App Store Slicing does per-device thinning automatically — ship your IPA and let Apple deliver only needed slices
  • Flutter's — split-debug-info works on iOS too
  • Keep your asset catalog tidy; prefer single-scale PDFs for vectorish assets where acceptable (Flutter rasterizes at runtime)

Build:

flutter build ipa --release --obfuscate --split-debug-info=build/symbols/2025-08-22

Start with artifact choice (ABI/AAB). Everything else is compounding gains

Field Notes (two quick stories)

Play warning disappeared overnight

After switching to per-ABI + AAB, Play's "size outlier" banner vanished on the next rollout. Install success rate ticked up +2.3% in low-storage regions

Support emails about "insufficient storage" dropped

We logged 38 → 9 such emails across the following week — same version, smaller payload

Build Cards You Can Paste Into CI

Android Release (AAB)

flutter clean
flutter pub get
flutter build appbundle --release --obfuscate \
  --split-debug-info=build/symbols/$(date +%F) \
  --tree-shake-icons

APK (side-load test)

flutter build apk --release --split-per-abi \
  --target-platform=android-arm,android-arm64 \
  --obfuscate --split-debug-info=build/symbols/$(date +%F) \
  --tree-shake-icons

Gradle (once)

minifyEnabled true
shrinkResources true

Sanity Checklist Before You Ship Smaller

  • Per-ABI or AAB (not universal)
  • R8 + resource shrinking on, ProGuard rules in place
  • — split-debug-info directory committed/uploaded to crash backend
  • — tree-shake-icons for Material/Icons
  • Assets listed precisely, heavy PNGs → WebP/AVIF
  • flutter pub deps scanned; remove zombie plugins
  • Deferred imports for rare, heavy features
  • Open the release on a low-end phone and measure install time + cold start

If you only do one thing today

Switch to AAB (or split-per-ABI APKs) and enable R8 + resource shrinking. That single combo fixes 80% of bloat in real apps

Drop your current size below and what changed after these steps — happy to help triage odd spikes or stubborn MBs

ps: built with Flutter + Firebase, indie-dev style — more breakdowns in my bio

#flutter, #flutterdev, #apk-size, #app-optimization, #android, #ios, #r8, #proguard, #aab, #split-per-abi, #tree-shake-icons, #performance

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