An easy way to resize contents in your WPF grid proportional to newsize of grid.

resize.cs

/*Assume that x:Name for Grid is myGrid in XAML*/
private void Window_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            myGrid.Width = e.NewSize.Width;
            myGrid.Height = e.NewSize.Height;

            double xc = 1, yc = 1; //xc = changed width referring to x axis, yc = changed width referring to y axis

            if (e.PreviousSize.Width != 0)
                xc = (e.NewSize.Width / e.PreviousSize.Width);
            if (e.PreviousSize.Height != 0)
                yc = (e.NewSize.Height / e.PreviousSize.Height);
        
            ScaleTransform scale = new ScaleTransform(myGrid.LayoutTransform.Value.M11 * xc, myGrid.LayoutTransform.Value.M22 * yc);
            myGrid.LayoutTransform = scale;
            myGrid.UpdateLayout();
        }