A class to help in adaptation of the sizes for widgets, texts, images, etc, on different screen sizes. In my case it uses a base designWidth = 411 because this is the width for my device used for development. Check yours with your designer or in your sketch / prototype.

dynamic_size.dart

import 'package:flutter/material.dart';

class DynamicSize {

  MediaQueryData _mediaQuery;
  static const double _designWidth = 411;

  DynamicSize._constructor();

  static final DynamicSize instance = DynamicSize._constructor();

  init(BuildContext context){
    _mediaQuery = MediaQuery.of(context);
  }

  double fromWidth(double width){
    var scaleWidth = _mediaQuery.size.width / _designWidth;
    var res = width * scaleWidth;
    return res;
  }
}