The present study deals with theoretical, experimental and numerical analysis of discharge coefficient for a rectangular sharp crested side weir in subcritical flow. De Marchi¿s modified spatially varied flow theory is used for the determination of discharge over the sharp crested side weirs. Assumption of same specific energy upstream and downstream is not valid for side weir with zero sill height. Downstream parameters influencing the coefficient of discharge are identified. The coefficient of discharge is found to be primarily a function of down stream Froude number and independent of ratio of sill height to the depth of water in downstream. Variation in coefficient of discharge as a function of down stream Froude number is found to exhibit a non-linear relationship. To avoid tedious trial and error procedure involved in the De Marchi equation for solving side weir problems, empirical equations are developed for easy solution of discharge over a side weir with finite sill height and zero sill height. Numerical analysis has been done to compare the results for diverted discharge through side weir and water surface profile along side weir obtained from experimental analysis.