Set column width in flutter

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,