Current guidelines suggest a minimum Kt/V of 1.2 for three weekly hemodialysis sessions; however, using V as a normalizing factor has been questioned. Parameters such as weight(0.67) (W(0.67)) and body surface area (BSA) that reflect the metabolic rate may be preferable. To determine this, we studied 328 hemodialysis patients (221 male) with a target Kt/V of 1.2. Using this relationship and the individual's Watson Volume, we calculated the Kt, Kt/BSA, and Kt/W(0.67) equivalent to the target and measured the effects of body size and gender on these parameters for each patient. The target corresponded to a range of equivalent Kt/BSA and Kt/W(0.67) each significantly higher in males than females and in larger than smaller males. V/BSA and V/W(0.67), the conversion factors of Kt/V to Kt/BSA and Kt/W(0.67) respectively, were significantly greater in males than females and heavier than lighter men. Our study shows that if Kt/BSA and Kt/W(0.67) reflect the true required dose, prescribing a target Kt/V of 1.2 would underestimate this in females and in small males. Further work is required to develop clinical outcome-based adequacy targets.