Pressure: the pressure of a centrifugal fan refers to the lift pressure (pressure relative to the atmosphere), that is, the increase of the pressure of the gas in the fan or the difference of the pressure at the inlet and outlet of the fan. It has static pressure, dynamic pressure, total pressure. Performance parameter refers to the total pressure (equal to the difference between the total pressure at the outlet of the fan and the total pressure at the entrance), and its units are usually Pa, KPa, mH2O and mmH2O.

Flow rate: the volume of gas flowing through the fan per unit time, also known as the air volume. The common units are; M3 /s, m3/min, m3/h (seconds, minutes, hours). (sometimes the "mass flow" is also used, that is, the mass of the gas flowing through the fan within a unit time. At this time, the density of the gas imported by the fan needs to be taken into account.