Total Body Water Calculator
Estimate the water in your body, the Watson way
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Total Body Water Calculator
Water is the largest single component of the human body. This calculator estimates your total body water (TBW) in litres and as a percentage of body weight using the validated Watson formula, which uses age, sex, height and weight. TBW is typically around 50–65% of body weight — higher in men and in leaner people, and lower when body fat is higher because fat holds little water. It is used in nutrition, kidney care and fluid management as a baseline reference.
Estimate using the Watson formula. Typical total body water is roughly 50–65% of body weight (higher in men and leaner people, lower with more body fat). Hydration needs and clinical use should be confirmed with a professional.
Frequently Asked Questions
- What is total body water and why does it matter?
- Total body water (TBW) is the total volume of fluid in your body, both inside and outside your cells. It's central to circulation, temperature control and nutrient transport, and typically makes up a little over half of adult body weight.
- How is total body water calculated?
- This calculator uses the Watson formula, which estimates TBW in litres from your age, sex, height and weight using sex-specific equations. Enter those four values and it returns your estimated litres of body water and that water as a percentage of body weight.
- What percentage of body weight should be water?
- Total body water is generally around 50–65% of body weight, typically near 50–55% for women and 55–65% for men, declining with age and higher body fat. Leaner, more muscular bodies hold a higher water percentage since muscle is water-rich.