Use LineHeight together with LineStackingStrategy="BlockLineHeight"
Like
<TextBlock Text="abcdefghijklmn" TextWrapping="Wrap" LineStackingStrategy="BlockLineHeight" LineHeight="30"/>
(credz Mixer for the BlockLineHeight addition)
Use LineHeight together with LineStackingStrategy="BlockLineHeight"
Like
<TextBlock Text="abcdefghijklmn" TextWrapping="Wrap" LineStackingStrategy="BlockLineHeight" LineHeight="30"/>
(credz Mixer for the BlockLineHeight addition)