The historical weather datasets of different locations of India were complied for solar radiation, maximum and minimum temperatures and sunshine hours. Solar radiation is vital parameter, measured only at 35 meteorological stations all over the India. Our country, with diverse agro climatic zones, although covered by huge network of 550 Automatic Weather Stations but still faces the problem of acquisition of data related to key meteorological parameters. This paper aims to calibrate the coefficient of two equations: 1) Angstrom Prescott Equation [Rs= (a+b*n/N) Ra], which has input of sunshine hours data 2) Supit–Van Kappel Equation [H=Ho (a √Tmax-Tmin +b√ (1- Cw/8) +c), with the inputs of easily available temperature and cloud cover data, on the basis of 25 stations all over India representing diverse agro climatic zones. Extrapolation technique was used for the stations that are located within radius of 200 km. The relationship of solar radiation with square root of the difference in maximum and minimum temperatures was significant. The northern region showed greater range of predictability, i.e. 0.43 to 0.86 in winter; 0.19 to 0.82 in pre monsoon; 0.25 to 0.84 in monsoon and 0.40 to 0.89 in post monsoon which was statistically significant. The degree of prediction was higher for locations in northern and western regions, which was poor for all location in southern and eastern regions. The transmissivity of the atmosphere for global solar radiation under perfectly clear sky conditions is given as the sum of the regression coefficient a & b of Angstrom Prescott Equation. Also, the transmissivity of an overcast atmosphere is interpreted as the value of the intercept, a. From our regression constants (a = 0.23 and b = 0.38), it is observed that the atmospheric transmissivity under clear skies is 0.61. This result compares well with the value of 0.67 to 0.70 reported for the humid tropics [4]. The clear-sky transmissivity of most tropical regions in general seems to lie between 0.68 and 0.75 [1, 8].