Hemodialysis (HD) is one of the treatments included in what is called the Renal Replacement Therapy (RRT). As every treatment, hemodialysis has its dose. How quantify this hemodialysis dosage was one of the results of the National Dialysis Cooperative Study (NCDS) published in 1983. A formula based in the Urea Kinetic Modeling (UKM) was developed. This formula was the dimensionless equation Kt/V where K is the dialyzer clearance rate of urea (or volume of plasma cleared), t is the duration of the dialysis session and V is the urea distribution volume (the total body water volume). Because of the complexity of urea kinetic modeling, a number of shortcut methods of estimating Kt/V have been proposed. The aims of this chapter are twofold: 1) to give an overview of single pool urea kinetic modeling and 2) to introduce concepts and methods needed to manage the approaches available to estimate the single pool Kt/V.