Objective: To calculate the mean free nasal airway space through specific measurements on lateral cephalogram and to correlate it with quantitative nasal air flow in nasal and oronasal breathers with three altered craniofacial morphological types. Methods: 90 subjects (45 males and 45 females) were divided into three groups:control group; Lip-incompetence group; long face group according to facial morphological criteria. They were again subdivided into three groups: Group I,II,III according to age groups. Each subject had undergone standard lateral cephalometric examination procedure and quantitative nasal air flow measurement using respiratory trnsducers. Linear and area measurement parameters were noted from lateral cephalometric tracings and different respiratory parameters were noted from respiratory cycle and compared. Results: There was significant correlation of Nasopharyngeal free airway space measured from Linear and Area measurements on a trapezoid on Lateral cephalometric tracings with different respiratory parameters used in this study. Conclusion: Ptm-ad2 should be routinely measured on lateral cephalogram to evaluate whether a patient suffers from obstruction of the nasal airway.