Guinness World Records has recorded no world record for the largest rattlesnake as of 2014. However, the Eastern Diamondback rattlesnake is the largest known species, and it grows up to 8 feet in length.
The largest reported Eastern Diamondback captured was in St. Augustine, Fla. However, many Internet sources exaggerated the actual size of the snake. Varied reports claimed the snake was 15 feet long, but its actual length was 7 feet 3 inches.
The Guinness world record for the largest captive snake goes to a reticulated python named Medusa. The python measured 25 feet 2 inches when it was measured on Oct. 12, 2011.