It is well-known that changes in micro-structure dimension (grain size) or in dislocation density (spacing) result in the Hall-Petch and Taylor forest-hardening effects respectively. Similarly, smaller test-piece dimension also showed a stronger response (micro-pillar). It is often understood that these length scales all contribute to the material strength governed by the same underlining mechanism, which is dislocation slip distance based. In the current theories, different dimensions are normally considered to act as obstacles in the same way to stop the dislocation motion. This hypothesis obviously has its weakness: a grain boundary can be overcome at higher stress but not a free surface. In this work, the individual length scale effect (e.g. grain size, pillar size, etc) will be studied separately when the key dimension is set to be equal, then compared to understand the strengthening ability of each length scale so that a more accurate combination method can be developed.