Titans remain very mysterious so far and elusive. Early on we see them as powerful warriors, like when Amir watches the giants troop by. Later we see them through Vilmos and others. RS speaks of Noman's power of illusion and how this allows them to pass without notice in the kingdoms. In the notes they are described as supreme giants but they don't seem to be much larger than men. This could be the work of the illusions and magics though when they are in the kingdoms. Hard to put a height to them though they are strong and skilled warrior people.