A new continuum approach to micro-mechanics of short fiber composites yielded two separate methods of estimating the apparent interfacial shear strength and fiber orientation efficiency. The methods exploit the compilation of the effects of fiber length distribution and interfacial shear strength on strengthening efficiency into a function of strain. The In-Built Method derives a unique combination of apparent interfacial shear strength and fiber orientation efficiency being able to reproduce the experimental stress-strain curve of a short fiber reinforced composite with a very low residual standard deviation. The Boundary Method accomplishes rapid interfacial shear strength screening in materials selection by constructing and utilizing the proposed selection chart. (C) Koninklijke Brill NV, Leiden, 2010