I did some googling out of curiosity, turns out Wikipedia has a whole ass article on it: The US prison rate as of 2021 is 531 per 100000 (peaked in 08 with 755 after a huge spike in the 80s and 90s, I wonder why). In the Soviet Union during the high of the gulag system, it was estimated (by actual historians, not the soviets) to be 714 to 892.
Apartheid South Africa was 851. Saudi Arabia has 200.