This paper presents design conditions due to the NTU of counter and cross flow type cooling tower. In the calculation of optimum design conditions for above two types which are widely used in our country, standard water-air ratio, ambient wet bulb temperature and bulk water temperature were adopted by domestic wheather conditions. The important result of this study is obtained as follows : Under the constant value of Ka and L, the number of transfer unit of cross flow type cooling tower Is about 1.1 times as large as that of counter, so the volume of cross flow type is about $10\%$ greater than that of counter.