Aim: To investigate the accuracy of fetal kidney length (FKL) in determining gestational age (GA) in the third trimester by ultrasound and comparing it with existing parameters. Materials and methods: This is an observational and comparative study conducted over a period of 1 year in the Department of Obstetrics and Gynecology of a tertiary care teaching hospital located in Puducherry, India. The study included pregnant women between 28 weeks and 34 weeks. All had a dating scan (DS) in the first trimester. The total study population was 100. All patients underwent a growth scan, and FKL was determined during the same. This value was compared with a normogram, and gestational age was determined. This was compared with the gold-standard gestational age derived from crown-rump length (CRL). The software used was MedCalc software. Results: The average FKL was positively correlated with CRL which was statistically significant (p <0.001). The Kappa analysis showed agreement of average FKL with CRL. Both sides of the kidney had comparable values, but the average length showed the best correlation to determine gestational age in the third trimester. Conclusion: The study showed that FKL is an accurate parameter to date pregnancy. It correlated well in combination with the other routinely used parameters for the estimation of gestational age in the third trimester. Clinical significance: The present study is one of the few studies conducted in the third trimester to date the pregnancy. It is applicable in low-resource settings where DS might not be available to accurately date the pregnancy.