Reinforced concrete structures utilize reinforcing bars to mitigate cracks and brittle fractures due to the relatively low tensile strength of concrete. Nevertheless, the infiltration of chloride into these structures can lead to the corrosion of the reinforcing bars. This study examines the corrosion process of reinforcing bars and determines the corrosion rate by applying Faraday’s law. The desired corrosion levels are achieved by applying a consistent current over a specified duration. The corrosion rate is calculated by measuring the weight loss due to corrosion relative to the overall volume of the reinforcing bar. Our objective is to analyze and compare corrosion rates determined through weight loss measurements versus those determined by cross-sectional area reduction of the bars. Experiments were conducted to compare these two methods, using reinforcing bar diameter and corrosion rate as variables. Results showed that the weight loss-based corrosion rate tests had a deviation of approximately ±10% from the calculated values. For corrosion rates up to 5%, the cross-sectional area loss-based corrosion rate tests exhibited a discrepancy of about 44.5% from the predicted values. However, for corrosion rates exceeding 5%, the difference decreased to 79.9–116.7%. A comparison of the two methods revealed that the discrepancy in corrosion rates decreased to less than 10% for corrosion rates above 5%. Therefore, it is concluded that for corrosion rates exceeding 5%, it is feasible to predict the corrosion rate using Faraday’s equation based on measurements of cross-sectional area loss. Future research should focus on improving the accuracy for corrosion rates below 5%, and it is anticipated that non-destructive testing methods for estimating rebar cross-sectional area could enable effective prediction of corrosion rates for structural assessment.