Usage patterns
〈物〉の個数を数えるto count the number of items
I counted the number of apples in the box.
個数を確認するto check/verify the quantity
Please check the quantity of items before shipping.
個数が合わないthe count doesn't match
I'm having trouble because the inventory count doesn't match.
個数制限a limit on the number of items
There's a limit of one sale item per person.