The largest living snakes in the world, measured either by length or by weight, are various members of the Boidae and Pythonidae families. They include anacondas, pythons and boa constrictors, which are all non-venomous constrictors. The longest venomous snake, with a length up to 18.5–18.8 ft (5.6–5.7 m), is the king cobra,^[1] while contesters for the heaviest title include the Gaboon viper and the Eastern diamondback rattlesnake. All of these three species reach a maximum mass in the range of 6–20 kg (13–44 lb).

There are fourteen or fifteen living snake species that clearly have a maximum mass of at least 50 lb (23 kg), as shown in the table below. Whether the number is fourteen or fifteen depends on whether a DNA analysis reported in 2024 results in the recognition of the northern green anaconda ("Eunectes akayima", listed in row 1b below) as a species distinct from the ordinary (southern) green anaconda (Eunectes murinus). These include all species that reach a length of at least 20 ft (6 m). There are also two other species that reach nearly this length – the Oenpelli python (binomial name Nyctophilopython oenpelliensis, Simalia oenpelliensis or Morelia oenpelliensis),^[2] and the olive python (Liasis olivaceus). The information available about these two species is rather limited.^[3] The Oenpelli python, in particular, has been called the rarest python in the world.^[4][5][6]

It is important to be aware that there is considerable variation in the maximum reported size of these species, and most measurements are not truly verifiable, so the sizes listed should not be considered definitive. In general, the reported lengths are likely to be somewhat overestimated.^[7] In spite of what has been, for many years, a standing offer of a large financial reward (initially $1,000 offered by U.S. President Theodore Roosevelt in the early 1900s,^[8] later raised to $5,000, then $15,000 in 1978 and $50,000 in 1980) for a live, healthy snake over 30 ft (9.14 m) long by the New York Zoological Society (later renamed as the Wildlife Conservation Society), no attempt to claim the reward has ever been made.^[3]

Although it is generally accepted that the reticulated python is the world's longest snake, most length estimates longer than 6 m (20 ft) have been called into question.^[7] It has been suggested that confident length records for the largest snakes must be established from a dead body soon after death, or alternatively from a heavily sedated snake, using a steel tape and in the presence of witnesses, and must be published (and preferably recorded on video).^[7] At least one reticulated python was measured under full anesthesia at 6.95 m (22.8 ft), and somewhat less reliable scientific reports up to 10.05 m (33.0 ft) have appeared.^[9]

Although weight is easier to measure reliably than length (e.g., by simply measuring the weight of a container with and without the snake inside it and subtracting one measurement from the other), a significant factor in the weight of a snake is whether it has been kept in captivity and provided an unusual abundance of food in conditions that also cause reduced levels of activity. Moreover, the weight of wild specimens is often reduced as a symptom of parasite infestations that are eliminated by veterinary care in captivity. Thus, the largest weights measured for captive specimens often greatly exceed the largest weights observed in the wild for the same species. This phenomenon may particularly affect the weight measurements for anaconda species that are especially difficult to keep in captivity due to their semi-aquatic nature, resulting in other species having larger weights measured in captivity. In particular, the green anaconda (Eunectes murinus) is an especially massive snake if only observations in the wild are considered.

Individual specimens considered among largest measured for their respective species include the following:

• Burmese pythons:
  • Wild caught (non-native invasive) Burmese python (Python bivittatus) female♀ 5.7912 m (19 ft 0 in) (19 ft) 56.699 kg (125.00 lb) caught in the Big Cypress National Preserve in eastern Collier County, Florida by Jake Waleri and Stephen Gauta on July 10, 2023. Waleri and several friends caught the large snake. They brought it to the Conservancy of Southwest Florida to have it officially documented. New current world record longest Burmese Python recorded by official measurement July 12, 2023.^[90][91][92]
  • "Baby" a captive Burmese python (Python bivittatus) female♀ 5.74 m (18 ft 10 in), 182.8 kg (403 lb); "Baby" was kept at Serpent Safari in Gurnee, Illinois, until its death at almost 27 years old, euthanized due to deteriorating condition caused by a tumor in 2006. Several live measurements and post mortem measurement.^[7][93]
  • "Hexxie" a captive Burmese python (Python bivittatus) female♀ 5.48 m (18.0 ft), 110 kg (240 lb) and still growing; "Hexxie" lives in a terraced house in Tewkesbury, Gloucestershire, England, with owner Marcus Hobbs.^[94][95][96]
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 5.39 m (17.7 ft), 98 kg (216 lb) and measured 64 cm (25 in) in diameter; She was carrying 122 developing eggs. Caught by a team of biologists in Everglades, Florida, June 22, 2022.^{[14][15][16][17]}
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) male♂ 5.23 m (17.2 ft), 94 kg (207 lb) and measured 66 cm (26 in) in diameter; caught by Okeechobee Veterinary Hospital, Florida, July 31, 2009.^[18][19][20]
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 5.72 m (18.8 ft), 47.2 kg (104 lb); caught in Miami-Dade County, Florida, October 2, 2020.^[97][98][99]
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 5.68 m (18.6 ft), 58.1 kg (128 lb); caught in Miami-Dade County, Florida, May 11, 2012. Intact specimen measured post mortem by University of Florida.^{[100][101][102]}
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 5.56 m (18.2 ft), 60.3 kg (133 lb); caught by University of Florida wildlife biologist in Miami-Dade County, Florida, July 9, 2015. Intact specimen measured post mortem by University of Florida.^{[103][104][105][93]}
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 4.57 m (15.0 ft), 65.3 kg (144 lb); caught by Nicholas Banos and Leonardo Sanchez, Everglades, Florida, April 1, 2017.^{[106][107][108][109]}
  • Wild-caught non-native (invasive) Burmese python (Python bivittatus) female♀ 5.2 m (17 ft), 63.5 kg (140 lb); she was carrying 73 developing eggs. Caught by Big Cypress National Preserve, Florida, April 7, 2019. ^{[110][111][112]}
• Reticulated pythons:
  • "Medusa" a captive reticulated python (Malayopython reticulatus) female♀ 7.67 m (25.2 ft) 158.8 kg (350 lb); "Medusa" is kept at the Edge of Hell haunted house attraction in Kansas City, Missouri, and was last officially measured in 2011.^[26][113]
  • "Samantha" a captive (originally wild-caught near Samarinda, Borneo, as an already very large adult) reticulated python (Malayopython reticulatus) female♀ 7.92 m (26.0 ft), somewhat reliable in 2002^[30][31]
  • "Fluffy" a captive reticulated python (Malayopython reticulatus) female♀ 7.3 m (24 ft) 136 kg (300 lb); "Fluffy" was last officially measured live on September 30, 2009, and died at the Columbus Zoo and Aquarium in Powell, Ohio, on October 26, 2010, due to an apparent tumor. She was 18 years old. 24 feet confirmed when measured at death.^[29][26]
  • "Colossus", a captive reticulated python (Maylayopython reticulatus) male♂, skeletal measurement 6.35 m (20.8 ft) 133.7 kg (295 lb); "Colossus" was kept at the Highland Park Zoo in Pittsburgh, Pennsylvania, died in April 1963, and the body was deposited at the Carnegie Museum.^[7]
  • "Twinkie" a captive reticulated python (Malayopython reticulatus) female♀ 7 m (23 ft 0 in) 156 kg (344 lb); "Twinkie" found sanctuary in the 2014 Guinness World Records book as the world’s largest albino python in captivity. She was a fixture at The Reptile Zoo in Fountain Valley, CA.^[27][28]
  • "Super Snake", a captive reticulated python (Malayopython reticulatus) 14-year-old female♀ 7 m (23 ft), 115 kg (254 lb); "Super Snake" is kept at the National Aquarium in Al Qana, Abu Dhabi, United Arab Emirates.^[32][33][34]
  • Wild-caught reticulated python (Malayopython reticulatus) Female♀ 7.5 m (25 ft) adjusted post-mortem measurement, unreliable, originally measured alive at 8 m (26 ft) unreliably, using an unknown method, 250 kg (550 lb) – estimated weight upon capture, unreliable; caught April 7, 2016, Paya Terubong district, Penang Island, Malaysia. Died April 10, 2016.^{[114][115][116]}
  • Wild-caught reticulated python (Malayopython reticulatus) unknown sex 7.8 m (26 ft), unverified; Was killed on October 5, 2017, Pekanbaru, Indonesia.^{[117][118][119]}
  • Wild-caught reticulated python (Malayopython reticulatus) unknown sex 6 m (20 ft), 80 kg (180 lb); Probably, this is largest snake in Phuket in last decade. Caught by Ruamjai Rescue Foundation, December 18, 2014, Phuket, Thailand.^{[120][121][122]}
• Australian scrub pythons:
  • "Maximus" a captive scrub python (Simalia kinghorni) male♂ 5.1 m (17 ft), 25 kg (55 lb), at the peak weighed about 27 kg (60 lb), when he was last weighed and measured in 2008; "Maximus" is believed to be the largest Australian native snake in captivity. He is kept at the Currumbin Wildlife Sanctuary on the Gold Coast, Queensland.^[123][124]
  • Wild-caught scrub python (Simalia kinghorni) unknown sex 5 m (16 ft), 28 kg (62 lb); caught by Machans Beach in Cairns, Queensland, November 14, 2017.^[125][126]
  • Wild-caught scrub python (Simalia kinghorni) unknown sex 5.1 m (17 ft), 27 kg (60 lb); caught by Speewah in Mareeba, Queensland, unknown date.^[127]
  • Wild-caught scrub pythons (Simalia kinghorni) unknown sex Both of were more 5 m (16 ft 5 in) (Second caught as stated measuring 5.1 m (16 ft 9 in) long and 27 kg (60 lb) in weight); caught by Speewah in Mareeba, Queensland, October 24, 2016.^[128][129]
  • Wild-caught scrub python (Simalia kinghorni) unknown sex 5.2 m (17 ft), 22 kg (49 lb); caught by Speewah in Mareeba, Queensland, February 6, 2017.^{[130][131][132]}

Wikispecies has information related to Reptilia.

• List of largest reptiles
• List of largest extant lizards
• Largest organisms
• Titanoboa, world's largest known snake from the fossil record
• Gigantophis, one of the world's largest snakes (past record holder for the world's largest known snake from the fossil record)