The seven hells, from fewest to most: the seventh, the sixth, the fifth, the fourth, the third, the second, the first.
Hell by hell, from the bottom: the seventh earth holds the fewest hell-beings; the sixth innumerably more; and so on up, each earth innumerably more populous than the one below it, to the first, Ratnaprabhā, which holds the most. Every rung is innumerable; what the ladder gives is the order, and it runs the opposite way from the earths' size in the lower world.
In the text's own words the ladder reads - fewest: the seventh; innumerably many times more: the sixth; innumerably many times more: the fifth; innumerably many times more: the fourth; innumerably many times more: the third; innumerably many times more: the second; innumerably many times more: the first. Source: Prajñāpanā 3.
The multitudes: fewest to most - By seven hells highlighted