The concentration ratio is most influential characteristic of the solar concentrators, impacting on its opto-thermal performance. Hence, concentration ratio's, realistic and quantificable measurement is essential. Therefore, this paper reveals the usefulness of the determination of an effective concentration ratio (Ceff) for a satellite antenna dish and Parvati concentrating solar cookers. Open and closed reflector open sun cooling tests were performed to determine the cooker opto-thermal ratio (COR). A thin black cloth used over each reflector neutralizes the effect of the reflection of solar radiation in the closed reflector tests. Subsequently, the COR values for these two types of tests enables the determination of the Ceff. Some corrective actions are suggested to eliminate the errors occurring during open reflector open sun cooling tests. Results show that the values of the Ceff for the satellite dish and Parvati cookers are 7.34 and 3.61, respectively. The determination of Ceff values enables commenting on its effective and realistic value, the role of the concentrator's reflecting surface in the concentration effect, and the degradation of the reflector surface. Thus, the Ceff is a practical indicator for assessing the impact of optical characteristics of the reflecting surface of the CSCs.