Cobras can vary in size depending on the species, but they can grow up to 18 feet (5.5 meters) long, with the average length being around 4 to 6 feet (1.2 to 1.8 meters). The king cobra, the world's longest venomous snake, can grow up to 18 feet (5.5 meters) long, while other species like the Indian cobra and the monocled cobra are smaller, typically growing to around 4 to 6 feet (1.2 to 1.8 meters) in length.