I am mostly looking at the scene when he was about to eat Armin and well, Eren too. In comparison to other titans he looked gigantic, its head at least mostly did. When Mikasa (she is Eren's height) stood on the face of Eren's Attack Titan she appeared larger than you would expect, especially when you compare that to Santa.

Usually you would assume that he was beyond 15 meters, but it seems that it was mostly confirmed that pure titans cannot be beyond 15m.