Volume deficit occurs in alloys during freezing and cooling due to decrease in specific volume and it is of major concern in the foundry industry. Volume deficit characteristic of cast Aluminium Silicon alloys has been discussed in the present study.Patterson and Engler have classified the volume deficit into four types namely, macro cavities, internal porosity, surface sinking and volumetric contraction. X-Ray computer tomography (XCT) is a more effective NDE tool in predicting the casting defects than conventional radiography. Quantification of internal closed porosity has been done through XCT.