The increasing demand and scarcity of water makes it important to use water in efficient way. The effective irrigation water management lays in proper estimation of crop water requirements, which are based on cropping pattern, rainfall in the area and other climatic factors. The water requirements of crop vary widely from crop to crop and also during the entire crop period of individual crop. In this present study firstly the reference crop evapotranspiration (ETO) has been estimated by using Penman-Monteith method. For this its estimation the mean monthly climatological and physiographical data for the year 2012 was used. Later crop water requirement for different crops in regional level i.e, for Vellore District was calculated on the basis of obtained ETO values. © 2015 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.