ABSTRACT: Background: The present study compared hounsfield unit of CT with grey scale value of CBCT for hypo and hyperdense structure. Materials & Methods:15 human dry skulls were subjected to MSCT and CBCT and hyperdense areas of enamel, cortical, and cancellous bones and hypodense areas of mental foramen, inferior alveolar canal and extraction socket within the mandible were assessed. Results: For extraction socket CT had -860.5 HU and CBCT had -740.5 grey scale, for mandibular canal CT had -560.2 HU and CBCT had -726.4 grey scale, mental foramen had CT of -432.6 HU and CBCT had -458.6 grey scale, cancellous bone had CT had 346.2 HU and CBCT had 416.2 grey scale and cortical bone had CT 1880.4 HU and CBCT had 1652.8 grey scale. The difference was significant (P< 0.05). Conclusion: The gray value for hypodense structures in large volume CBCT scan was more reliable and analogous to HU value in MSCT.