Background: In detecting fetal abnormalities & intrauterine growth retardation, the ultrasound measurement of fetal dimensions is very helpful. Even in women with reliable dates, the error in gestational age(GA) calculation can occur, thus accurate assessment of GA by sonography is of great importance. For diagnosis, investigation & treatment of fetus in vitro estimation of GA by ultrasonography is of high clinical importance. Aims: To find out the least variable parameter for estimation of fetal gestational age & to see whether a single parameter can be applied over whole pregnancy period to avoid the confusion in interpretation of gestational age. Materials & Methods: The present hospital based observational study was conducted at government tertiary hospital of Jammu. All the participants were explained purpose of study & informed consent was taken from every participant prior to study. After meeting inclusion & exclusion criteria all the patients underwent complete history, examination & ultrasonography. Results: Among 200 participants maximum number of participants i.e. 95 were seen in age group of 23–26yrs followed by 53 in 27–30yrs. A total of 69 participants had weight 61–65kgs whereas height of 155–158cms was found in 116 participants. Maximum no.of cases closest to Naegle’s rule were estimated by biparietal diameter (146) followed by femur length but femur length showed least deviation from Naegle’s rule. Conclusion: From the present study it has been concluded that both femur length & bi–parietal diameter are equally efficient estimators of fetal gestational age but femur length showed a slight edge over BPD in normal overall pregnancy