Rainfall is the most important and an essential natural source of water, which is utilized for different purposes.Hydrological analysis and modelling becomes very popular in the field of water resources management. Rain gauge is a common instrument that is used to measure the amount of rainfall and it also provides the rainfall distribution pattern.These data prove to be very useful and can be used for different purposes, such as design of hydraulic structures, flood control, irrigation canal design, etc. Thus, rainfall data are prime input parameter and it is most critical for a river basin to have an optimum number of rain gauges in catchment area of the river. This paper has basically analyzed whether the Sabarmati River basin has an optimum number of rain gauges or not. If not then design of optimum number of rain gauge is an important task in the river basin. Thus, according to IS:4987-1994, Optimum number of rain gauges in Sabarmati river basin is 37, while existing rain gauges are 31. So, Additional 6 rain gauges are required in basin and their location is also proposed in this paper based on Thiessen polygon method, which is used for equal areal rainfall distribution in the basin.