The report, titled "The ASCE Standardized Reference Evapotranspiration Equation," is authored by the Task Committee on Standardization of Reference Evapotranspiration of the Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE). The primary goal of this report is to standardize the calculation of reference evapotranspiration (ET) and provide a consistent basis for determining or transferring crop coefficients for agricultural and landscape use. The standardized equation is based on the ASCE Penman-Monteith (ASCE-PM) method, which is applied to two types of reference surfaces: clipped grass (short, smooth crop) and alfalfa (tall, rougher crop). The equation is simplified to a reduced form suitable for hourly and daily calculations. The report provides guidelines for assessing weather data integrity and estimating missing values. It also includes detailed computational procedures, tables, and equations for calculating various meteorological variables such as net radiation, soil heat flux, and wind speed adjustments. The standardized equation is intended to simplify the calculation process and ensure reproducibility and transferability of ET estimates. The report is endorsed by the Irrigation Association and has been developed in response to a request from the association to establish a benchmark reference evapotranspiration equation.The report, titled "The ASCE Standardized Reference Evapotranspiration Equation," is authored by the Task Committee on Standardization of Reference Evapotranspiration of the Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE). The primary goal of this report is to standardize the calculation of reference evapotranspiration (ET) and provide a consistent basis for determining or transferring crop coefficients for agricultural and landscape use. The standardized equation is based on the ASCE Penman-Monteith (ASCE-PM) method, which is applied to two types of reference surfaces: clipped grass (short, smooth crop) and alfalfa (tall, rougher crop). The equation is simplified to a reduced form suitable for hourly and daily calculations. The report provides guidelines for assessing weather data integrity and estimating missing values. It also includes detailed computational procedures, tables, and equations for calculating various meteorological variables such as net radiation, soil heat flux, and wind speed adjustments. The standardized equation is intended to simplify the calculation process and ensure reproducibility and transferability of ET estimates. The report is endorsed by the Irrigation Association and has been developed in response to a request from the association to establish a benchmark reference evapotranspiration equation.