Kt/V is one of the reference methods by which the amount of dialysis given is measured. Kt/V, like the URR, focuses on urea as the target solute, and is based on the assumption that removal of urea is from a single space – "urea distribution volume", or formula_2 similar in capacity to the total body water. The urea distribution volume formula_2, although traditionally thought of as 60% of body weight, may actually be closer to 50% of the body weight in women and 55% in men with stage V (GFR < 15 ml/min) chronic kidney disease. The clearance of urea during the dialysis session formula_4 can be expressed in either formula_5 or formula_6. Time or formula_7 is the duration of the dialysis session, measured either in minutes or hours. So formula_8 is also a volume, either formula_9, or formula_10, and represents the volume of blood (in ml or L) cleared of urea during the dialysis session. Because formula_2 is also a volume, the ratio of formula_12 has dimensions of formula_13 or formula_14, making it a "dimensionless" ratio.