how to change size appbar flutter code example

Example 1: flutter how to find the appbar size

var height = AppBar().preferredSize.height;

Example 2: Flutter: Setting the height of the AppBar

appBar: PreferredSize(
  preferredSize: Size.fromHeight(100.0),
  child: AppBar(
    automaticallyImplyLeading: false, // hides leading widget
    flexibleSpace: SomeWidget(),
  )
),