According to the ranking system developed by the U.S.-based Council on Tall Buildings and Urban Habitat, the Eureka Tower qualified as the tallest building in three of the four categories in which heights are ranked, namely height to the floor of the highest occupied floor of the building. For comparison, the Q1 apartment tower on the Gold Coast has its highest habitable floor (the observation deck), reaching a height of , some lower than Eureka Tower's highest habitable floor. Q1's highest penthouse apartment is whilst Eureka's penthouse is high. However, the spire attached to the top of Q1 exceeds the Eureka Tower in the other two categories, namely "Height to the tip of spire, pinnacle, antenna, mast or flag pole" – in this case, spire – and height to architectural top of the building.