To measure volumetric flow rate, use a flow meter. Cubic feet is a unit of volume, and minute is a unit of time. The rate of volume flow is referred to as volumetric flow rate.
Volumetric flow meters come in various forms. Some rely on gravity and have spherical balls inside conical tubes. As air flows through this type of flow meter, the ball rises, and graduations on the outside of the device indicate the volume of fluid flowing through the meter.
Other flow meters have dial indicators that provide observers with analogue readings of the rates of flow. Flow meters with digital readouts are also widely available as of 2015. These types of flow meters are called positive displacement flow meters. Some flow meters do not measure flow rate directly but instead infer flow rate using pressure differentials. These types of meters are called inferential flow meters.
Flow meters generally require that the fluid flowing through them be free of debris and laminar. Turbulent flow can cause inaccurate readings, as can particulate. As a result, it is generally recommended that flow meters are installed as far from fittings as possible and that particulate filters are upstream of the flow meters.