This study evaluates the effect of mis-positioning of patients in relation to the iso-centre in CT examinations on the dose received by phantoms with various diameters. Phantoms with water-equivalent diameters (Dw) ranging from 8.5 cm to 42.1 cm were scanned using a GE Optima CT scanner with exposure factors as follows: 200 mA, 120 kVp, 1.375 Pitch, 50 cm field of view (FOV), 5 mm beam collimation, and 1 s rotation time. Doses were measured using the CT dose profiler (RTI Electronics). After obtaining doses in every hole of the phantoms, weighted doses were computed. It is found that the dose decreased with an increase in the Dw. The ratio of the doses when positioned off-centre by 2 cm and 4 cm with respect to the iso-centre have p-values of 0.914 and 0.919, which shows no significant difference (p> 0.05).