This paper presents a full-field analysis of size dependent crystal plasticity according to two robust and efficient ways to account for microstructural internal length effects in the constitutive laws. Both consist in introducing a Hall–Petch term in the definition of the resolved shear stress. They differ by the nature of the internal length and thus, intrinsically, on the scale at which this size dependency is introduced. In the meso-scale approach, it is directly the size of the considered grain. In the micro-scale approach, it is the distance to the grain boundary. Analyses show that meso- and micro-scale differences increase as the grain size distribution evolves from a unimodal to a bimodal one.