In this paper, we will describe the methodology used to conceive and size a flowmeter for two-phase dispersed flows. The Venturi having been chosen as the velocity measurement device, we focus on its measurement sensitivity to the velocity slip between the phases at the throat. Among the different two-phase flow models reviewed, an original one has been selected and adapted to predict; velocity and pressure distributions along a Venturi tube with air/water and oil/water flows. Bubble and liquid velocity calculations performed by this model are compared with experimental data to show a good agreement between predicted and measured velocities al the throat. The superiority of this model is shown by comparing its pressure drop predictions with those obtained with more classical two fluid models and available experimental data. Finally the influence of the bubble diameter on the pressure drop calculations and flow rate evaluations has been studied to determine the maximum admissible bubble diameter and then to size the mixer set upstream of the Venturi.