DART

flutter appbar width

appBar: AppBar(
          title: Text('AppBar Height'),
          toolbarHeight: 100.0, // double
          automaticallyImplyLeading: false, // hides back button
        ),

height appbar flutter

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

flutter add height to appbar

appBar: PreferredSize(
  preferredSize: Size.fromHeight(200.0),
  child: AppBar(
    automaticallyImplyLeading: false,
    flexibleSpace:  Image(
              image: AssetImage('assets/images/banner_image.jpg'),
              fit: BoxFit.cover,
            ),
            backgroundColor: Colors.transparent,
  )
),

change app bar height flutter

AppBar(
   title: Text('Flutter is great'),
   toolbarHeight: 100,
  ),