GetWidgetWidthAndHeiget.dart

import 'package:flutter/material.dart';

class GetWidgetWidthAndHeiget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  final GlobalKey globalKey = GlobalKey();

  void _getWH() {
    final containerWidth = globalKey.currentContext.size.width;
    final containerHeight = globalKey.currentContext.size.height;
    print('Container widht is $containerWidth, height is $containerHeight');
  }

  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size;
    final width = size.width;
    final height = size.height;
    print('width is $width; height is $height');
    return Scaffold(
      appBar: AppBar(
        title: Text('Width & Height'),
      ),
      body: Center(
        child: Container(
          key: globalKey,
          color: Colors.redAccent,
          width: width / 2,
          height: height / 2,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _getWH,
        child: Icon(Icons.adjust),
      ),
    );
  }
}