A 20-band sp(3)d(5)s* spin-orbit-coupled, semiempirical, atomistic tight-binding model is used with a semiclassical, ballistic, field effect transistor (FET) model, to examine the ON-current variations to size variations of [110]-oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3 to 12 nm are examined and significantly different behavior in width versus height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the full band model here show that ON-current doubling can be observed in the ON-state at the onset of volume inversion to surface inversion transport caused by structural side size variations. Strain engineering can smooth out or tune such sensitivities to size variations. The cause of variations described is the structural quantization behavior of the nanowires, which provide an additional variation mechanism to any other ON-current variations such as surface roughness, phonon scattering, etc.