Mechanical flow meters use fluid movement to drive a rotating assembly with proportional rotational speed to flow rate. It is important to consider mechanical design elements in creation of a flow meter, as these characteristics dictate the performance and accuracy of the meter. The first mechanical characteristic to consider in designing a mechanical flow meter is impeller size. Impeller size influences the minimum and maximum flow rate capable of being measured. Use flow rate simulation software to evaluate the effectiveness of the mechanical system, and the impeller size can be adjusted accordingly to realize the desired sensing range.

Primary sources of inaccuracy originate from losses in the mechanical assembly. Frictional losses in the rotating impeller influence the linearity of sensing across the sensed flow range. Additional losses are attributed to disruptions in fluid flow from the rotating mechanical assembly. Such losses are typically more difficult to evaluate without simulation software, or physical flow meter testing. Ideally, output frequency linearly correlates with flow rate, though losses can force low and high flow rates to deviate from the linear sensing range. Software adjustment can be used in some cases to account for non-linearity in flow rate measurement.