This study reexamines the literature data on performance of louvered inertial classifiers and offers a preliminary correlation of particle fractional collection efficiency, eta. These classifiers incorporate a converging array of blades to intercept the inlet particle-laden gas and separate it into major and minor flows. A basic design concept in such classifiers is that particles, with larger Stokes number St, follow the minor flow for collection. The correlation is for rectilinear classifiers, with flat plate louvers, in turbulent flow where pressure loss is independent of Reynolds number. The fractional collection efficiency near 0.5, with 0.2 < (St)(1/2) < 1.0, increases with log(St(1/2)). The respective influences of orientation, chord and spacing of the louvers and the converging profile of the louver array are examined. (C) 2017 Elsevier B.V. All rights reserved.