Background: Accurate estimation of foetal weight in late pregnancy and labour is extremely useful in the management of labour and delivery. It helps obstetricians in making decisions about appropriate mode of delivery, trial of labour, planned vaginal breech delivery, instrumental vaginal delivery and trial of labour after caesarean delivery all with the aim of reducing the morbidity and mortality associated with birth trauma and perinatal asphyxia. Clinical formulae and sonographic estimation are the two common methods of foetal weight estimation. However the superiority of sonographic estimation over the clinical methods has been a source of debate. Also there are concerns about the influence of some biological variables such as maternal BMI and actual birth weight categories on the accuracy of both methods of foetal weight estimation. Aim: The aim of this study is to determine and compare the accuracy of clinical estimation of foetal weight using Dare’s formula with that of sonographic estimation using hadlock 3 formula. Also the influence of maternal BMI and actual birth weight categories on the accuracies of these methods was determined. Study design/Setting: A prospective comparative study conducted at the University of Ilorin Teaching Hospital. Methods: Three hundred consenting and eligible pregnant women planned for either vaginal delivery or caesarean section were recruited for the study using systematic random sampling. Data collection sheet was used to obtain information on socio-demographic characteristics, clinical parameters and sonographic parameters. The patient’s height and weight were measured and the BMI was calculated. In-utero clinical estimation of foetal weight was carried out using a flexible tape measure calibrated in centimetre to measure the symphysio-fundal height and abdominal girth at the level of the umbilicus and the product of the two was calculate as the foetal weight in grammes. The patients also had sonographic estimation of foetal weight using Hadlock 3 formula in the foetal assessment unit. After delivery, the newborn babies were weighed within 30 minutes of delivery. Outcomes measured include estimated foetal weight error, absolute estimated foetal weight error, absolute percentage error, and absolute percentage error less than 10% (i.e. an estimated foetal weight that is within ±10% of the actual birth weight) for both clinical and sonographic methods of estimation. Comparison was made using the chi-square test and student’s t-test, where necessary. Subgroup analysis based on Preset BMI categories and ABW categories was done to assess the influence of BMI and ABW on the accuracy of both clinical and sonographic estimation of foetal weight. A p-value of < 0.05 was taken as statistically significant.