[0cf8612b2e1e]

How many characters tall is a Japanese book? English paperbacks seem to be similarly sized on the number of characters/words wide. Interface guidelines put an optional number of characters on a screen somewhere between 60-80. Books being taller than they are wide seem like it would stretch the limit to something harder to track for vertical writing.

[franciscop]

Note that Japanese characters are much bigger (+ meaning-packed) than Latin characters, so it's also harder to lose track of which line you are at IMHO.

[Macha]

Like 20ish seems common in my experience learning. But you have to consider that most words are 1-3 characters before comparing that to English line lengths.