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Total Body Water (Watson Formula)

The Watson formula estimates total body water from sex, age, height and weight (men: 2.447 − 0.09516·age + 0.1074·height + 0.3362·weight; women: −2.097 + 0.1069·height + 0.2466·weight). It is commonly used as the urea distribution volume V in dialysis Kt/V.

  • Age (years)
  • Sex: Male; Female
  • Height (cm or m or in)
  • Weight (kg or lb)
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Formula

Men: TBW = 2.447 − 0.09516 × age + 0.1074 × height (cm) + 0.3362 × weight (kg). Women: TBW = −2.097 + 0.1069 × height + 0.2466 × weight.

Clinical pearls

  • Derived in healthy adults by isotope dilution; overestimates TBW in obesity less than weight-fraction rules, but is not validated in oedematous or critically ill patients.
  • For quick bedside sodium and free-water calculations, a weight fraction (0.6 men, 0.5 women; less in elderly) is usually used instead.

Examples

total body water watson 40 yo male 175 cm 80 kgwatson tbw for a 60 year old woman 165cm 60kg

FAQ

Why does the Watson formula ignore age in women?

In Watson's regression age did not add meaningful prediction for women, so the female equation uses only height and weight.

What is TBW used for?

Dialysis adequacy (Kt/V), drug and alcohol distribution volume, and sodium/free-water deficit calculations.

Evidence

  1. 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;33:27–39.

General & Anthropometrics · Reviewed 2026-10-14 · Methodology