The main objective of this study is to obtain correlations for the optimum tilt angle of solar collectors in Erzurum, Turkey. The monthly average solar energy data of the concerned region are required for the design of a solar energy system. The values of the monthly average daily total solar radiation incident on a horizontal surface are nearly available. However, the radiation values on tilted surface, required for various studies, are generally not available. This article deals with the correlations of the optimum tilt angle of solar collectors for solar energy applications. An application of the model was performed using the solar radiation data measured for Erzurum in Turkey. The optimum angle for tilted surface varying from 0 to 90 degrees was calculated by searching for the values of which the daily total solar radiation was a maximum for a specific period.