Specimens of ''S. amethistina'' have reportedly been measured at more than {{convert|8.5|m|ft|1|abbr=on}} in total length (including tail), but this is exceptional, as {{convert|4|m|ft|abbr=on}} specimens are already considered extremely large. Although, the amethystine python is smaller than the Australian scrub python, some sources claim, that ''S. amethistina'' able to reach length in {{convert|5.5|m|ft|abbr=on}} and mass of {{cvt|20|kg}}<ref name="Daniel Natusch">{{Cite journal|first1=Daniel |last1=Natusch |first2=Jessica |last2=Lyons |first3=Richard |last3=Shine |year=2022|journal=[[Scientific Reports]] |title=Spatial ecology, activity patterns, and habitat use by giant pythons (Simalia amethistina) in tropical Australia|volume=12|issue=1|url=https://www.researchgate.net/publication/359517466|doi=10.1038/s41598-022-09369-5 |pmid=35347214 |pmc=8960824 |bibcode=2022NatSR..12.5274N }}</ref> and even {{cvt|35|kg}}.<ref>{{cite journal|first1=Daniel |last1=Natusch |first2=Jessica |last2=Lyons |first3=Lea-Ann |last3=Mears|first4=Richard |last4=Shine |year=2020|publisher=Department of Biological Sciences, Macquarie University |title=Biting off more than you can chew: attempted predation on a human by a giant snake (''Simalia amethistina'') |url=https://research-management.mq.edu.au/ws/portalfiles/portal/167828778/134330879_AAM.pdf |journal=[[Austral Ecology]] |volume=46 |number=1 |pages=159–162 |doi=10.1111/aec.12956 }}</ref> However, the largest specimen has length of {{convert|4.72|m|ft|abbr=on}}.<ref name="Harvey2000"/>
The smooth [[dorsal scales]] are arranged in 39–53 rows at midbody. There are deep heat-sensing pits on six or seven of the posterior lower labials.<ref>[[George Albert Boulenger|Boulenger GA]] (1893). ''Catalogue of the Snakes in the British Museum (Natural History). Volume I., Containing the Families ... Boidæ ...'' London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). xiii + 448 pp. + Plates I–XXVIII. (''Python amethystinus'', pp. 83–84).</ref>
