Ferroelectric and ferroelastic domains can be reoriented during the application of electric field through domain wall motion. This study develops a method to quantify the domain reorientation in perovskite ferroelectrics with orthorhombic crystal lattices. In situ, high-energy X-ray diffraction was utilized to obtain intensity ratios that are necessary for the calculation. Domain reorientation in orthorhombic Li-doped Na0.5K0.5NbO3 is then quantified using this method. The preference of domain orientations is explained by considering the angle between spontaneous polarization of the respective domains and the applied electric field direction. The extent of domain reorientation increases as the Li substitution increases which additionally correlates to increased piezoelectric coefficient d (33) and field-induced strain. Increased domain wall motion is further proposed to originate due to the increased compositional proximity to the morphotropic phase boundary, a proposed universal behavior in ferroelectric compositions-containing phase boundaries.