“总人数”常见的英文表达是 “total number of people” 或 “total headcount”（“headcount”更常用于统计员工或特定群体数量）。
The total number of people attending the conference is over 500.（参加会议的总人数超过500人。）
We need to confirm the total headcount for the event by next week.（我们需要在下周前确认活动的总人数。）