Body Water Calculator
Water Is the Largest Component of Body Weight
More of your body weight is water than anything else — more than fat, more than muscle protein, more than bone mineral. That share isn't fixed: it shifts with age, sex, and body composition, since fat tissue holds much less water than lean tissue does. The Watson formula estimates total body water directly from age, height, and weight without requiring a bioimpedance scale.
The Formula
Watson Formula:
Men: TBW (L) = 2.447 − (0.09156 × Age) + (0.1074 × Height cm) + (0.3362 × Weight kg)
Women: TBW (L) = −2.097 + (0.1069 × Height cm) + (0.2466 × Weight kg)
Men: TBW (L) = 2.447 − (0.09156 × Age) + (0.1074 × Height cm) + (0.3362 × Weight kg)
Women: TBW (L) = −2.097 + (0.1069 × Height cm) + (0.2466 × Weight kg)
Worked Example
| Sex | Total body water | % of body weight |
|---|---|---|
| Male | 43.7 L | 58.3% |
| Female | 35.1 L | 46.8% |
The gap between sexes at the same height and weight reflects the higher average body-fat percentage in women, since fat tissue is roughly 10–15% water compared to about 70–75% for muscle tissue.
Why Total Body Water Is Tracked
- Hydration and fluid therapy — clinicians use body water estimates as a starting point for calculating fluid replacement needs.
- Interpreting scale weight swings — a 1–2 kg day-to-day weight change is far more often water shifting than actual fat gained or lost.
- Body composition context — a body water percentage that's unusually low for age and sex can flag higher relative fat mass even before a dedicated body fat test.
How to Use This Calculator
- Choose Metric (kg/cm) or Imperial (lb/in) units.
- Select your sex.
- Enter your age, weight, and height.
- Select Calculate to see your estimated total body water in liters and as a percentage of body weight.
Related Calculations
Set a daily fluid target with the Water Intake Calculator, or see how body water fits into overall composition with the Body Fat Calculator.