Wikipedia cities a number of sources for between 130K and 60K:
> One conquistador, Andrés de Tapia, was given the task of counting the skulls on the "tzompantli" at Tenochtitlan and estimated that there were 136,000 skulls on it.[17] However, based on numbers given by Taipa and Fray Diego Durán, Bernard Ortiz de Montellano[18] has calculated that there were at most 60,000 skulls on the "Hueyi Tzompantli" (Great Skullrack) of Tenochtitlan. The "Hueyi Tzompantli" consisted of a massive masonry platform composed of “thirty long steps” measuring fully 60 meters in length by 30 meters wide at its summit. Atop of the aforementioned platform was erected an equally formidable wooden palisade and scaffolding consisting of between 60 and 70 massive uprights or timbers woven together with an impressive constellation of horizontal cross beams upon which were suspended the tens of thousands of decapitated human heads once impaled thereon.[19] There were at least five more skull racks in Tenochtitlan but by all accounts they were much smaller.
> One conquistador, Andrés de Tapia, was given the task of counting the skulls on the "tzompantli" at Tenochtitlan and estimated that there were 136,000 skulls on it.[17] However, based on numbers given by Taipa and Fray Diego Durán, Bernard Ortiz de Montellano[18] has calculated that there were at most 60,000 skulls on the "Hueyi Tzompantli" (Great Skullrack) of Tenochtitlan. The "Hueyi Tzompantli" consisted of a massive masonry platform composed of “thirty long steps” measuring fully 60 meters in length by 30 meters wide at its summit. Atop of the aforementioned platform was erected an equally formidable wooden palisade and scaffolding consisting of between 60 and 70 massive uprights or timbers woven together with an impressive constellation of horizontal cross beams upon which were suspended the tens of thousands of decapitated human heads once impaled thereon.[19] There were at least five more skull racks in Tenochtitlan but by all accounts they were much smaller.
https://en.wikipedia.org/wiki/Tzompantli#Aztec