Replacing my bathroom exhaust fan and totally confused about CFM ratings. The current fan is super weak and doesn't do much. Looking at new fans but they range from 50 CFM to 150+ CFM. How do I know what I need? 💨

My bathroom is about 80 sq ft. Internet says different things - some say 1 CFM per sq ft, others say different formulas. Plus some fans are way more expensive - is it worth getting a higher CFM fan?

Also considering one with a humidity sensor so it turns on automatically. Good idea or gimmick? Current fan has a switch that we forget to turn on half the time.