A character or a monster is considered Gargantuan when they stand 32 to 64 feet tall while weighing 16 to 125 tons. Such creatures usually take up a 20 ft. by 20 ft. space and have 15 ft. reach if they are long and 20 ft. reach if they are tall.
A Gargantuan creature gets a -4 size penalty to Armor Class and attack rolls, a +12 size bonus to grapple checks and a -12 size penalty on Hide checks. A Gargantuan creature’s carrying capacity is 8 times as good as that of a Medium character (12 times for quadrupeds). A Gargantuan creature uses much larger weapons than a Medium character.
Those a bit smaller than Gargantuan size are considered Huge, those a bit bigger are called Colossal,those twice as big as Gargantuan are called Humongous, and those even BIGGER are known as Titans