What Is CFM?
CFM (cubic feet per minute) measures how much air a fan, duct, or ventilation system moves. This calculator estimates the CFM needed to achieve a target number of full air changes per hour in a room.
The Formula
First the room volume is found: volume = length × width × height. Required airflow is then CFM = (volume × air changes per hour) / 60, since air changes per hour describes how many times the entire room’s air is replaced in sixty minutes.
Recommended air-change rates vary widely by space type (a bathroom, kitchen, and mechanical room all differ), so this tool is meant as a general planning reference. For code-required ventilation rates, consult your local building code or an HVAC professional.
Last reviewed August 2026