The crop water requirement (CWR) and irrigation requirement (IR) of watermelon was calculated using a web based software. Relevant crop coefficients (Kc), duration of crops and cropping pattern were used to calculate CWR from ETo. These coefficients present the relationship between references (ETo) and crop evapotranspiration (ET crop) or ET crop = Kc * ETo. The covered area of all crops (canopy cover) was collected. The Kc values were taken from FAO. The CWR were calculated for the north central plateau zone of Odisha for which climatic data were available and were applied to the nearest Research station. The effective rainfall was calculated with web based software by using FAO conversion table. The CWR and IR value was also calculated through this web based software Water requirement of watermelon, is 343 mm and Irrigation requirement of this crop is 271 mm. in this zone 2. By using the software a farmer of this zone can find out the water requirement and irrigation requirement by giving the crop name according to their season and duration of crop.