The study aims at investigating the imaging and sizing capabilities of ultrasonic phased arrays and the synthetic aperture focusing technique (SAFT) of surface-breaking defects in a carbon steel plate. The defects were imaged using a phased array transducer and the relative arrival time technique (RATT) was used to size the defects. Studies were carried out to size near-through-wall defects so as to estimate the largest size of defect that can be accurately sized in accordance with the leak before break (LBB) criterion in critical applications. Additionally, the study also aims at sizing the smallest defect that can be sized accurately using the two techniques. The study also shows a direction for improved sizing accuracy of certain defects by means of the hybrid-based genetic algorithm (GA) approach which otherwise was limited by the two imaging techniques.