how to change font size of flutter material button?

The widget architecture in Flutter makes this very simple: The child of the MaterialButton is a Text widget, which can be styled with its style property:

new MaterialButton(  height: 140.0,  minWidth: double.infinity,  color: Theme.of(context).primaryColor,  textColor: Colors.white,  child: new Text(    "material button",    style: new TextStyle(      fontSize: 20.0,      color: Colors.yellow,    ),  ),  onPressed: () => {},  splashColor: Colors.redAccent,);

You can make use of the style attribute of your Text widget.

MaterialButton(  ...  child: Text(    'material button',    style: TextStyle(      fontSize: 20.0, // insert your font size here    ),  ),)

just using the official docs TextStyle & fontSize

https://api.flutter.dev/flutter/painting/TextStyle-class.html

https://api.flutter.dev/flutter/painting/TextStyle/fontSize.html

fontSize default to 14 logical pixels, double

final double fontSize;

demo

import 'package:flutter/material.dart';void main() => runApp(App());class App extends StatelessWidget {  @override  Widget build(BuildContext context) {    return MaterialApp(      // home: StateApp(),      home: Scaffold(        appBar: AppBar(          title: Text("appbar"),          backgroundColor: Colors.blueAccent[700],        ),        body: Center(          child: StateApp(),        ),      ),    );  }}class StateApp extends StatefulWidget {  StateApp();  @override  createState() => _StateAppState();}class _StateAppState extends State<StateApp> {  int _counter = 0;  _updateCounter() => setState(() {    _counter++;  });  // _updateCounter() {  //   setState(() {  //     _counter++;  //   });  // }  @override  Widget build(BuildContext context) {    return Scaffold(      body: Center(        child: Column(          children: <Widget>[            Padding(              padding: const EdgeInsets.all(23.0),// double              child: Text(                'You have pushed the button this many times:',                style: TextStyle(                  fontWeight: FontWeight.bold,                  fontSize: 18.0,// double                ),              ),            ),            Center(              child: Text(                '$_counter',                style: TextStyle(                  fontWeight: FontWeight.bold,                  fontSize: 23.0,// double                ),              ),            ),          ],        ),      ),      floatingActionButton: FloatingActionButton(        onPressed: () {          // _counter++;          print("clicked = $_counter");          // setState(() {          //   _counter++;          // });          _updateCounter();        },        child: Icon(Icons.add),      ),    );  }}