Urea Volume of Distribution (Vd) Calculator
Estimates Vd for urea as total body water (TBW) using the Watson equation (default) or a simple rule‑of‑thumb. Answer the five questions below and press Calculate.
Notes & Assumptions
- For urea, Vd ≈ total body water (TBW). Watson’s anthropometric equation estimates TBW in litres. The simple rule‑of‑thumb approximates TBW as a proportion of body weight.
- Results are estimates for adults in steady state. Edema, ascites, obesity, cachexia, pregnancy, and acute shifts of body water can make TBW deviate from these formulas.
- This tool is for education and research support. It is not a substitute for clinical judgment.
Formulae
Watson (1980) TBW (L):
- Male: TBW = 2.447 − 0.09156 × age (y) + 0.1074 × height (cm) + 0.3362 × weight (kg)
- Female: TBW = −2.097 + 0.1069 × height (cm) + 0.2466 × weight (kg)
Simple rule‑of‑thumb: Adult male TBW ≈ 0.6 × weight (kg); adult female TBW ≈ 0.5 × weight (kg).
References
- Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr. 1980;33(1):27–39.
- Rowland M, Tozer TN. Clinical Pharmacokinetics and Pharmacodynamics: Concepts and Applications. 5th ed. Wolters Kluwer; 2019. (Urea distributes in total body water; Vd ≈ TBW).
- Brunton LL, Hilal‑Dandan R, Knollmann BC, eds. Goodman & Gilman’s The Pharmacological Basis of Therapeutics. 13th ed. McGraw‑Hill; 2018. (Distribution of small hydrophilic molecules such as urea).