The ASCE Standardized Reference Evapotranspiration Equation was developed by the Task Committee on Standardization of Reference Evapotranspiration of the Environmental and Water Resources Institute of the American Society of Civil Engineers. The equation is based on the ASCE Penman-Monteith method and is designed to provide a standardized basis for calculating reference evapotranspiration (ET) and transferring crop coefficients for agricultural and landscape use. The equation is simplified to a reduced form of the ASCE-PM method and is applicable to two types of reference surfaces: clipped grass (short crop) and alfalfa (tall crop). The standardized equation includes fixed constants and standardized computational procedures, making it relatively simple to apply and widely accepted by the scientific and engineering communities. The equation is used to calculate ET for daily and hourly time steps, with specific calculations for vapor pressure, net radiation, and wind speed adjustment. Guidelines are provided for assessing weather data integrity and estimating values for missing data. The standardized equation is intended to simplify and clarify the presentation and application of the method, and it is recommended for use in calculating reference evapotranspiration and, in turn, crop evapotranspiration. The equation is also recommended for developing new crop coefficients and facilitating the transfer of existing crop coefficients. The equation requires measurements or estimates for air temperature, humidity, solar radiation, and wind speed. These parameters are considered to be the minimum requirements to estimate ET for short and tall reference surfaces. The equation is applicable to a wide range of locations and climates across the United States and has been investigated over a wide range of locations and climates. The standardized equation has been accepted as a reliable method for calculating reference evapotranspiration and is recommended for use in agricultural and landscape irrigation. The equation is also recommended for use in developing new crop coefficients and facilitating the transfer of existing crop coefficients. The equation is designed to provide a standardized basis for determining or transferring crop coefficients for agricultural and landscape use.The ASCE Standardized Reference Evapotranspiration Equation was developed by the Task Committee on Standardization of Reference Evapotranspiration of the Environmental and Water Resources Institute of the American Society of Civil Engineers. The equation is based on the ASCE Penman-Monteith method and is designed to provide a standardized basis for calculating reference evapotranspiration (ET) and transferring crop coefficients for agricultural and landscape use. The equation is simplified to a reduced form of the ASCE-PM method and is applicable to two types of reference surfaces: clipped grass (short crop) and alfalfa (tall crop). The standardized equation includes fixed constants and standardized computational procedures, making it relatively simple to apply and widely accepted by the scientific and engineering communities. The equation is used to calculate ET for daily and hourly time steps, with specific calculations for vapor pressure, net radiation, and wind speed adjustment. Guidelines are provided for assessing weather data integrity and estimating values for missing data. The standardized equation is intended to simplify and clarify the presentation and application of the method, and it is recommended for use in calculating reference evapotranspiration and, in turn, crop evapotranspiration. The equation is also recommended for developing new crop coefficients and facilitating the transfer of existing crop coefficients. The equation requires measurements or estimates for air temperature, humidity, solar radiation, and wind speed. These parameters are considered to be the minimum requirements to estimate ET for short and tall reference surfaces. The equation is applicable to a wide range of locations and climates across the United States and has been investigated over a wide range of locations and climates. The standardized equation has been accepted as a reliable method for calculating reference evapotranspiration and is recommended for use in agricultural and landscape irrigation. The equation is also recommended for use in developing new crop coefficients and facilitating the transfer of existing crop coefficients. The equation is designed to provide a standardized basis for determining or transferring crop coefficients for agricultural and landscape use.