What is water weight?
Water makes up a large share of total body weight, typically somewhere between 45% and 65% depending on age, sex, and body composition. Muscle tissue holds more water than fat tissue, which is why the percentage differs between individuals of the same weight.
How this calculator works
This calculator uses the Watson formula, a well-established equation from clinical and sports science research for estimating total body water from age, sex, height, and weight. Men generally have a higher total body water percentage than women, mainly due to typically higher lean muscle mass and lower body fat percentage.
The result shows your estimated water weight in kilograms and as a percentage of your total body weight. Day-to-day changes on a scale are often driven more by short-term shifts in body water (from hydration, sodium intake, exercise, or hormonal cycles) than by actual fat gain or loss.
This is a population-based estimate for general educational purposes, not a direct measurement. Methods like bioelectrical impedance analysis or clinical dilution testing provide more precise individual results.