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A size comparison of various snakes living and extinct. Comparing large individuals of the green anaconda (Eunectes murinus) and reticulated python (Malayopython reticulatus) to length estimates of the extinct Palaeophis colossus, Gigantophis garstini, Vasuki indicus and Titanoboa cerrejonensis.

There is often uncertainty over the maximum size possible or the largest reliably recorded individuals for living animal species, generally due to unreliable visual estimations or lack of hard evidence. Accurately measuring the overall length of a snake is difficult. Various methods exist, but all have issues. Therefore, researchers might disagree with what they consider the largest reliable recorded size for a given species, and/or the sizes shown here might not represent the true maximum for the species. It is also important to note that the largest recorded sizes often represent exceptional individuals and do not represent the average size.

Extinct snakes are often known from fragmentary remains, so length estimates must be extrapolated using living species or more complete relatives. However, due to the large number of variables, these estimates can vary substantially between methods and should be treated with caution. Due to the lack of complete remains, the morphology of the extinct snakes is uncertain. P. colossus has been restored here with a small paddle at the end of the tail, a feature common in marine snakes. However, due to lack of remains this feature is speculative.

• The green anaconda is generally considered the most massive extant snake. The silhouette is scaled to 5.21 metres (17.1 ft), the longest individual out of ~780 anacondas measured around a cattle ranch by Jesús Antonio Rivas. There are reports of exceptionally large anacondas, some claimed up to 9 to 11 metres (30 to 36 ft), but these are controversial. Rivas cast doubt on the existence of exceptionally large anacondas due to factors such as constraints on body size and breeding ability. However, they suggested that sizes larger than those observed in study area may be possible in habitats with permanent water bodies and little human intervention. In 2024, a large anaconda was found dead in Bonito, Brazil, which was reportedly measured at 6.32 metres (20.7 ft). However, this has yet to be published in an academic journal.

• The reticulated python is considered the longest extant snake but is usually less massive relative to the green anaconda. The silhouette is scaled to 6.95 metres (22.8 ft), which is the length of a reliably measured wild reticulated python. Larger sizes have been reported, some claims reach up to ~10 metres (33 ft) in length, but these are considered controversial or unreliable. A captive reticulated python named "Medusa" was reported to measure 7.67 metres (25.2 ft).

• Gigantophis garstini is a large member of the extinct snake family Madtsoiidae. Gigantophis is known from numerous vertebrae. In 2004, it was estimated between ~9.3 and 10.7 metres (31 and 35 ft) in length by Jason Head & P. David Polly using regression analysis (10 metres (33 ft) shown here). A later study by Jonathan P. Rio & Philip D. Mannion used a regression analysis that compared the vertebral postzygapophyseal width to the total length in extant boine snakes. This regression estimated the largest vertebra of the Gigantophis type specimen at ~6.9 metres (23 ft) (+/- 0.3 m). However, the authors urged caution due to uncertainties regarding the possible position of the vertebra in the spinal column, the lack of articulated madtsoiid remains, and the possibility that Gigantophis and extant boine snakes differ in the relationship between postzygapophyseal width and total length.

• Palaeophis colossus is an extinct species of marine snake in the family Palaeophiidae. One vertebra, CNRST-SUNY 290, produced a length estimate of 8.1 metres (27 ft), comparing the trans-prezygapophyseal width to a variety of extant snake species. Using a different vertebral landmark, the cotylar width, another vertebra NHMUK PV R 9870, produced a length estimate of 12.3 metres (40 ft).

• Titanoboa cerrejonensis is an extinct boid only known from large vertebrae and skull material, but size estimates suggest it is one of the largest snakes known. In 2009, Jason Head and colleagues estimated it at ~12.8 metres (42 ft) (+/-2.18 m) by regression analysis that compared vertebral width against body lengths for extant boine snakes. In a later conference abstract, Head et al. estimated a length of ~14.3 metres (47 ft) (+/-1.28 m) based on skull material and comparisons to anacondas.

• Vasuki indicus is a large Madtsoiidae snake known from several large vertebrae. Datta & Bajpai applied two existing length estimation regressions on these vertebrae, producing estimates ranging from 10.9 and 12.2 metres (36 and 40 ft) and 14.5 and 15.2 metres (48 and 50 ft) (11.5 and 14.8 metres (38 and 49 ft) shown here). However, due to the incompleteness of the remains and limited knowledge of Madtsoiidae snake vertebral columns, Datta & Bajpai urged caution with the estimates.

• Human scaled to 180 cm (5 ft 11 in).