The water is most precious thing on the Earth. The agriculture sector is main user of available fresh water on the earth. We have to use water optimally and if crops are irrigated optimally then yield will be more. In the paper we have, implemented Evapotranspiration based Smart Irrigation System for Agriculture. The system is implemented using online weather parameters, data from moisture sensor and Raspberry pi. Estimation of crop water requirements (ETc) is one of the major parameter used in automated irrigation system. The prediction of Reference Evapotranspiration (ETo) is based on meteorological variables like temperature, humidity, daily sunshine hours, wind speed. By applying a crop coefficient (Kc) values from standard FAO document, we can estimate Crop Evapotranspiration (ETc) using estimated value of this ETo. In this paper, two standard methods are used as "Blanney Criddle method"and "Modified Penman method"to estimate value of reference Evapotranspiration ETo). We have implemented system to determine reference evapotranspiration (ETo) and crop Evapotranspiration (ETc) for Wheat Kharif crop for Pune region. The system is implemented using online weather parameters, data form moisture sensor and Raspberry pi. The data from moisture sensor and crop water requirement (ETc) is used to estimate actual need of irrigation for selected crop and water pump will be automatically ON/ OFF. © 2022 ACM.