Scale the text using a ScaleTransform

   
  


<Window x:Class="SDKSample.Window1"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="Text Transform Samples"
  Background="FloralWhite"
  Height="640">

    <StackPanel>
      <TextBlock FontSize="32" FontWeight="Bold" Foreground="SteelBlue" Text="asdf" Margin="100, 0, 0, 0">
        <TextBlock.RenderTransform>
          <ScaleTransform ScaleX="1.5" ScaleY="1.0" />
        </TextBlock.RenderTransform>
      </TextBlock>
      <TextBlock FontSize="32" FontWeight="Bold"  Foreground="SteelBlue"
        Text="{Binding Path=Text, ElementName=textblockScaleMaster}"
        Margin="100, 0, 0, 0">
        <TextBlock.RenderTransform>
          <ScaleTransform ScaleX="1.0" ScaleY="1.5" />
        </TextBlock.RenderTransform>
      </TextBlock>
    </StackPanel>
</Window>