Many renal disorders are associated with changes in the size of the kidneys, normative standards for assessing renal size is essential as it shows variability in the values of normal renal size depending on body size, age and ethnicity and for comparison when examining renal disease. Ultrasound is usually the first imaging modality use in evaluating the kidneys for pathology. The aim of this study is to determine the renal size of normal adult population. This was a prospective cross sectional study conducted over a period of 10 months (January-October 2016) on the kidneys of 390 normal adults aged >18 years. The length, width, depth, volume, cortical thickness and parenchymal thickness of both kidneys were measured using ultrasound. The mean right and left renal size was 139±34.2cm 3 and 173.7±13.5cm 3 respectively. The difference in size was statistically significant. In males, the mean right renal size was 140.2±33.7 cm 3 while the mean left renal size was 183±48.9cm 3 . In females, mean right renal size was 138.6±34.8cm 3 while the mean left renal size was 164.3± 47.7cm 3 . There was a positive correlation between renal size and age, side, body mass index (BMI) and body surface area (BSA). Normative values of renal size in an adult Nigerian population have been established. Renal size correlated with age, sex, BMI and BSA. Body habitus, age, sex, and side should be taken into consideration when reporting the renal size of normal adults.