As many massive concrete structures are being constructed, efforts to reduce the hydration heat of cement and thermal cracking in mass concrete are being made. To analyze the temperature change of mass concrete, it is very important to evaluate the thermal characteristics of concrete such as the final adiabatic temperature rise and reaction factor. Owing to cost-effectiveness, for evaluating the effect of mixture design to reduce hydration heat of concrete, semi-adiabatic temperature rise tests are more widely used than the adiabatic temperature rise test. To develop an equation to compensate temperature loss for the semi-adiabatic test, Newton’s law of cooling was used in this study. A constant k-value in Newton’s law of cooling can cover not only the effect of thermal conductivity and specific heat of concrete and insulation surrounding concrete but also the thermal condition of the floor and the convection coefficient of the test room. For the proposed predictive equation, the effect of specimen size was also considered to reflect the effect of the heat value according to different specimen volumes. By compensating the temperature loss using the rate of cooling at each stage, not only the final adiabatic temperature rise and reaction factor but also the hysteretic temperature curve of concrete in other studies could be well predicted.