The staggered herringbone mixer was studied using computational fluid dynamics (CFD) and particle tracking methods. The positions of tracer particles as well as the stretching of a fluid element associated with each tracer particle were tracked using a fourth order Runge-Kutta integration scheme with adaptive time stepping. Striation patterns observed were in qualitative agreement with experimental work from literature. The computed stretch values were found to be log-normally distributed. The specific stretch per period for a spatially periodic flow was computed. This allows for an estimation of the required length for complete mixing by further accounting the penetration depth achieved by molecular diffusion. The microchannel lengths for complete mixing computed using the mean stretch were lower than those obtained experimentally. This was attributed mainly to the fact that the experimentally derived values were measured in the central 50% of the mixer cross-section where striation thickness reduction can be observed to be slower. Furthermore, the specific stretch per period represents the mean stretch value while in reality the stretch values are distributed log-normally. In the design of mixers, a conservative estimate of the required mixing length can be obtained by replacing the mean stretch per period with a value which represents the cut-off point for the lower 10% of the distribution. The design lengths computed using these values were slightly higher than experimental ones and found to exhibit the same trend with increasing Peclet number. The pressure drop at various Re was also investigated and was found to be slightly lower than that of an equivalent grooveless channel. (c) 2008 Elsevier B.V. All rights reserved.