Even though smartphones today come with increasingly larger storage every year — most now ship with 64–128GB (2020) — developers must always remember that this space isn’t reserved solely for our apps. That storage belongs to users: for their photos, videos, and important documents that shape their daily lives. This is precisely why app size matters, and it’s something Flutter has consistently prioritized. Whether it’s introducing tree-shaking — starting with icons so that only the ones you actually need get bundled in release builds, sparing users from unnecessary downloads — or going further in Flutter 1.22 with a brand-new tool to diagnose exactly which parts of your code contribute to the final app size. That tool is the App Size Tool, found under the Analysis tab in DevTools.

The App Size Tool breaks down your app’s size into three categories: Dart code, Native code, and non-code components bundled within your app, such as assets and fonts. The Dart code figure represents the final compiled output when you build in Release or Profile mode. Dart uses AOT (Ahead-of-Time) compilation instead of JIT, with tree-shaking already applied to strip out as much unused code as possible.

How do I use it?

If DevTools is connected to a running app, you can navigate straight to the App Size tab. If DevTools isn’t currently connected to an app, you can also access it from the DevTools home screen.

Analysis Tab

This tab lets you analyze the size of a snapshot you’re interested in, displaying the data as both a treemap and a table. You can drill down for more details — such as why a particular piece of code ended up in your compiled app — using the Dominator Tree and Call Graph.

Diff Tab

The Diff tab allows you to compare the sizes of two files side by side, typically from two different versions of your app. The comparison is again presented as both a treemap and a table.

For more details about the App Size Tool, visit https://flutter.dev/docs/development/tools/devtools/app-size. For additional information about compiled app size, see https://flutter.dev/docs/perf/app-size#breaking-down-the-size.

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