Three models developed for calculating the monthly average daily total horizontal solar radiation anywhere in Turkey have been comparatively studied with monthly averages of the values measured via pyranometer in 11 stations. Comparison study has been done according to the values of mean quadratic error, mean absolute error, and correlation coefficient. In the statistical tests, it has been seen that the most successful model belongs to one developed by Ogelman et al. It has been established that new models could be investigated on a basis of the data collected through 11 stations.