R factor or erosivity factor is one of the parameter for computation of soil loss using Universal soil loss equation and its value depends upon intensity, duration, velocity and drop size of rainfall. The R factor is usually calculated from high resolution (very small time interval) rainfall data. But the process of calculation of R factor from high resolution rainfall data is very tedious and also the rainfall data of small time interval are not available everywhere. So, in this study, we developed the FORTRAN program based on equation of Wischmeier and Smith to calculate the value of erosivity factor (R-factor) using the 10 minute interval rainfall data. calculation was performed using the rainfall data of eight years from 2007 to 2014 which were obtained from the meteorological site (http://www.kma.go.kr) for the eight different cities of different provinces of Korea. After obtaining r-factor from the rainfall data, regression equation was developed for each province which can be used to predict the value from the monthly rainfall data without running the model. Appropriate regression curve was selected for each province using the software “CurveExpert“. This web based model is very simple to use and it can be very effective tool to estimate the parameter R-factor of USLE.