Abstract In this study, the solar radiation variation on horizontal surfaces calculated by the ASHRAE clear-sky model is compared with measurements for Erzurum, Turkey (latitude: 39.55; longitude: 41.15; altitude: 1,869 m). A daily total solar radiation is obtained by integrating the hourly distribution. The results show that the ASHRAE clear-sky model is suitable to estimate hourly solar radiation in Erzurum, Turkey. Also, correlations giving the monthly average clear sky solar radiation on horizontal surfaces are developed. In addition, mean bias error, root mean square error, and t-statistic methods are used to indicate model performance.