This paper describes the design and implementation of a unit substation demand estimator (USDE). The paper presents various methods for the estimation of missing data measurements in a 4kV distribution network. Each method is tested in detail to validate the accuracy of the estimated data and an estimation process strategy is suggested. By using the successive estimation methods and Microsoft Excel macro commands (Visual Basic for Application code) a USDE application is developed. The USDE application is then tested on field data and special tuning functions are developed to improve the estimation process.