China is coy about the actual numbers, but US Asst Sec of Defense for Indo-Pacific Affairs estimates that as many as 3 million people are being held in the reeducation camps (link below). That alone is already more than the total US prison population. Even if you prefer to go with the more conservative estimates (which are mostly around 1-2 million), that's more than the US prison population when combined with the 2 million or so Chinese in traditional prisons.
https://www.reuters.com/article/us-usa-china-concentrationca...