How to increase/decrease the size of Raised button

Raised buttons have a minimum size of 88.0 by 36.0

To increase/decrease the size of raised button , wrap the raised button in a container or in sized box and give them the desired height and width.

For Example->

SizedBox(
  width: 100,   // specific value
  height: 40.0, // specific value
  child: RaisedButton(
  onPressed: () {},
    child: Text("Hello Everyone"),
),
),

or

Container(
  width: 100,
  height: 40.0, 
  child: RaisedButton(
   onPressed: () {},
    child: Text("Hello Everyone"),
),
),

Now the Raised Button will have width as 100 and height as 40.

Another better Option is to use ButtonTheme

ButtonTheme(
  minWidth: 100.0,
  height: 100.0,
  child: RaisedButton(
    onPressed: () {},
    child: Text("Hello Everyone"),
  ),
);