Solar radiation data, a prerequisite for the designing and sizing of solar energy systems, are not available in many Indian locations. However the sunshine hour or temperature data are available for most sites from which solar radiation can be computed. New correlation models have been developed; incorporating the latitude and altitude of a site to estimate the monthly average global solar radiation on horizontal surfaces using the sunshine hour and temperature data. The models are used for computing values of six Indian stations with different geographical locations, based on 10-15 years of data. The estimated values are found to be in close agreement with their measured values. The estimated data are also compared with the results using other models to test the accuracy of new models. It has been shown that the estimated values of global radiation using temperature data are also sufficiently accurate and can be utilized for sites for which even sunshine hour data are not measured. This will lead to better inputs for designing and evaluating the performance of solar energy systems including passive solar buildings.