The gear flow meter is a type of Positive Displacement flow meter used to measure the volumetric flow of liquids. Positive Displacement flow meters directly measure the volume that passes through the meter rather than the velocity or some other physical characteristic of the liquid to calculate the volumetric flow rate, making them a volumetric meter. Volumetric meters directly measure the total volume passing through the meter rather than measuring the velocity of the flow or inferring the volumetric flow rate from some physical characteristic such as the conductivity or sound velocity. The advantage of volumetric meters over inferential or velocity meters is that the viscosity effects are largely removed. Fluids like oils and greases can be measured at very low flow rates where the other technologies require much higher minimum flow rates and so are ineffective for real world application rates.

The gear principle is a simple concept: two shaped rotors, with integral timing gear teeth around their perimeters, rotate within a precision measuring chamber. The rotors are installed at exactly 90 degrees from each other, and this relationship is maintained as they rotate. The Gear Meter requires no external timing mechanism, making it a simple device with only 2 moving parts that are durable and easily serviceable. Each rotation of the Gear rotors will transmit 4 identical volumes of liquid from the meter inlet to outlet providing either a constant number of electronic pulses to a digital instrument, or 360 degrees of rotational motion to a mechanical counter. They are well suited for a broad range of applications and excel in many operating conditions where other measurement principles cannot be used effectively, or at all.