The weight of a jellyfish depends on the species. One of the more common species, the deadly box jellyfish, can weigh up to about 5 pounds.
One of the largest breed of jellyfish, the giant Nomura's, can reach up to 450 pounds when fully grown. These jellyfish are found off the coasts of Japan and China. The largest recorded specimen was a lion's mane jellyfish found on the shore of Massachusetts Bay in 1870. The body measured more than 7 feet with 120-foot tentacles. Its size prohibited a proper assessment of its weight. There are approximately 1,500 species of jellyfish, ranging in length of less than one millimeter to 80 inches.