Number + も
as many as, a whole … (emphasis)
Number + counter + も
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も after a number stresses that it's a lot, more than expected: 駅で一時間も待ちました, "I waited at the station for a whole hour"; このかばんは十万円もした, "this bag cost as much as 100,000 yen".
It's the same も as "also", stretched: "even as much as".
The opposite feeling, "only", is しか with a negative (一時間しかない) or だけ.
With a negative verb, a number with も means "not even": 一人も来なかった, "not a single person came"; 一度も行ったことがない, "I've never been, not even once". Either way, the も adds emphasis.
Examples
駅で一時間も待ちました。
I waited at the station for a whole hour.
このかばんは十万円もしました。
This bag cost a whole 100,000 yen.
昨日はビールを五杯も飲んだ。
I drank five whole beers last night.
毎日十時間も働いています。
I'm working a whole ten hours a day.
三回も電話したのに、出なかった。
I called three times, and you still didn't pick up.