Usage patterns
〈人〉の人数を数えるto count the number of people (in a group)
I counted the number of participants.
人数が多いto have a large number of people; a big crowd
This school has large class sizes.
人数を制限するto limit the number of people (allowed)
This event limits the number of attendees.
人数が足りないto not have enough people
We don't have enough people to play soccer.
人数がそろうfor the full number of people to be present
Everyone came, and we finally had the full group.