Gurren Lagann
The size of mecha can vary according to the story and concepts involved. Some of them may not be considerably taller than a tank ("Armored Trooper Votoms", "Megazone 23", "Code Geass"), some may be a few stories tall ("Gundam", "Escaflowne", "Bismark", "Gurren Lagann"), others can be as tall as a skyscraper ("Space Runaway Ideon", "Genesis of Aquarion", "Neon Genesis Evangelion"), some are big enough to contain an entire city ("Macross"), some the size of a planet ("Diebuster"), galaxies ("Getter Robo", "Tengen Toppa Gurren Lagann"), or even as large as universes ("Tengen Toppa Gurren Lagann: Lagann-hen", "Demonbane", "Transformers: Alternity").