Standard Fan Sizing Bathroom vent fans are rated for the amount of air they can move, measured in cubic feet per minute, or CFM. Standard fan sizing applies to bathrooms that are 100 square feet or less. The rule of thumb is that you need at least 1 CFM per square foot of room area.Click to see full answer. Herein, how many CFM do I need for my bathroom fan?Most fans are rated from 50 to 110 CFM. For bathrooms 50 square feet and smaller, it is recommended you purchase a bath fan designed for small rooms, which will typically have a CFM range of 50-79. For bathrooms that are larger, select a fan that can move at least 1 CFM per square foot of room.Similarly, is it better to have a higher CFM? Larger fans can move more air with less noise. Depends on the application. Higher static pressure more suited to CPU coolers or radiators with dense fins. For cases fans higher CFM is better and as already said a larger slower rotating fans will have good CFM at a lower noise level (as a rule). Likewise, how do I calculate CFM for exhaust fan? In general, to calculate CFM for your industrial exhaust application, you need to know the total floor area of your space. With this number, divide it by multiply it by 0.1 to 1 to get you estimated CFM. For example, a 1000 square foot area may need a CFM exhaust fan of 1000*0.1=100 or 1000*1=1000.What is the best brand for bathroom exhaust fan? Best Bathroom Fan Reviews – Top Picks Delta Breez SLM70 Slim 70 CFM Exhaust Fan. Broan 678 Ventilation Fan. Broan 688 Ceiling and Wall Mount Fan. Panasonic FV-11VH2 Bathroom Exhaust Fan With Heater. Broan 655 Bathroom Exhaust Fan With Heater. iLiving ILG8SF7V Wall-Mounted Exhaust Fan.