A new method to calculate the average value of the rate of striation thinning, alpha, from the laminar flow field in a static mixer as simulated by Computational Fluid Dynamics (CFD) has been developed. The shape of the developing striations is inferred by executing a particle tracking procedure to the CFD flow field obtained. Problems arising from the complex trajectories and their translation to Ottino's (The Kinematics of Stretching, Chaos and Transport, Cambridge University Press, Cambridge, UK, 1989) micromixing theory have been solved. The method has been applied to mixer configurations with Kenics and SMX elements. Laser induced fluorescence experiments showed good agreement to model results when visually comparing the striation distribution patterns. The distribution of a values throughout the mixer could thus be calculated. The average value of a turns out to be constant per element. We have thus demonstrated that a micromixing theory could be adequately coupled to the accurate description by CFD of the flow pattern inside a reactor with local resolution.