Set column width in flutter

I need to set a Column width in flutter, I have to do a layout with 3 sections, one should be 20% of the screen, the other one 60% and the last one 20%. I know that those 3 columns should be into a row, but I don't know a way to set the size, when I do that, the 3 columns take the same size.

I will appreciate any feedback.

Instead of hard-coding the size, I would suggest using Flex like

Row(
      children: <Widget>[
        Expanded(
          flex: 2, // 20%
          child: Container(color: Colors.red),
        ),
        Expanded(
          flex: 6, // 60%
          child: Container(color: Colors.green),
        ),
        Expanded(
          flex: 2, // 20%
          child: Container(color: Colors.blue),
        )
      ],
    )

Which will produce like below,

Limiting the width of a Column could be

1. Limiting the width of Column itself, use SizedBox

   SizedBox(
     width: 100, // set this
     child: Column(...),
   )
   

2 (A). Limiting width of children inside Column, without hardcoding values

Row(
  children: <Widget>[
    Expanded(
      flex: 3, // takes 30% of available width 
      child: Child1(),
    ),
    Expanded(
      flex: 7, // takes 70% of available width  
      child: Child2(),
    ),
  ],
)

2 (B). Limiting width of children inside Column, with hardcoding values.

Row(
  children: <Widget>[
    SizedBox(
      width: 100, // hard coding child width
      child: Child1(),
    ),
    SizedBox(
      width: 200, // hard coding child width
      child: Child2(),
    ),
  ],
)