Evapotranspiration data are available from lysimeters, field plot sampling and other methods for a variety of crops at various locations. At a given location there is frequently considerable spread or scatter in the data. This paper presents formulas and methodology for estimating evaporation equivalent to Class A pan evaporation from a standardized exposure, for estimating potential evapotranspiration. from climatic data, for estimating actual or normal evapotranspiration from evaporation or from potential evapotranspiration, and for estimating irrigation requirements.