Formability of metals and alloys in general and aluminium alloys and steels in particular is of paramount importance in sheet metal forming in automobile industry. It is well understood that the evolution of preferred crystallographic orientation of crystallites or texture during prior thermo-mechanical processing of sheets plays an important role in determining formability. The formability of sheet is measured in terms of the Lankford parameter or the plastic strain ratio which is defined as the ratio of strain in width direction to that in the thickness direction (R = εw/εt). The variation of Lankford parameter with the rolling direction and standard and ΔR value is widely used in industry as a standard for estimating the formability of the rolled sheets. In the present investigation, we have used the viscoplastic self-consistent simulations to theoretically calculate the variation of the Lankford parameter with rolling direction for different crystallographic texture in model face centre cubic and body centre cubic material. It is observed that crystallographic texture obtained from unconventional processing routes like dissimilar speed rolling or asymmetric rolling and change in strain path strongly influence the evolution of R value thereby affecting the formability of the unconventionally rolled sheets.