The 副助詞（ふくじょし） (adverbial particle) も
is often used for labeling (A) as part of a category, when it would not usually be considered part of that group. In this way, it emphasizes that (A)’s inclusion is something that is surprising/unexpected in some way.
is used after a specific number + counter, it shows that the number itself is surprising. This can be when the actual number is lower, or higher than what was expected. Due to this, も
can translate as ‘as much as (A)’, or ‘not even (A)’, and other similar phrases in this expression.
I worked as long as 12 hours, so I am tired.
That cellphone cost you as much as 200,000 yen?!
I have never taken the subway, not even once.
At first glance, this may seem different than も
’s translation as ‘too’ or ‘also’, but in those cases, も
is also just pointing out the something unexpected is part or whatever group was initially highlighted.
I want to go too.
The above sentence just shows that the (B) speaker is unexpectedly putting themselves in the group that the (A) speaker initially only considered themselves to be a part of.