Body Water Calculator

The calculator uses the Watson formula, developed by Dr. P.E. Watson in 1980, which estimates total body water (TBW) from your age, height, weight, and sex. For males: TBW = 2.447 − 0.09156 × age + 0.1074 × height (cm) + 0.3362 × weight (kg). For females: TBW = −2.097 + 0.1069 × height (cm) + 0.2466 × weight (kg). This formula was validated against direct measurement methods and remains one of the most widely cited in clinical medicine.

Males typically have a higher proportion of muscle mass, which holds more water than fat tissue. Females generally have a higher body fat percentage, which contains very little water. This is why males tend to have a higher body water percentage (around 60%) compared to females (around 50–55%), even at the same weight and height.

Watson's research found that in males, body water percentage decreases measurably with age — mainly due to changes in muscle mass and fat distribution over time. In females, this age-related change was not statistically significant enough to be included in the formula, so height and weight alone are sufficient predictors.

For a typical healthy adult male, body water accounts for about 55–65% of total body weight. For females, it's typically 45–60%. Newborns have the highest proportion at around 75%, while older adults tend to have lower percentages due to reduced muscle mass. The exact amount varies based on fitness level, age, and body composition.

For males, a body water percentage between 50–65% is considered healthy. For females, 45–60% is typical. Values below the lower end may suggest dehydration or high body fat, while values above the upper range can reflect very high muscle mass. These are estimates — clinical conditions should always be evaluated by a healthcare professional.

Staying well hydrated by drinking adequate water daily is the most direct approach. Building lean muscle mass through regular exercise also increases your body's water content, since muscle tissue is roughly 75% water. Reducing excess body fat — which contains very little water — can also shift your body water percentage upward over time.

In hot or tropical climates, you lose more water through sweat, which can temporarily lower your total body water if fluid intake doesn't compensate. The body tightly regulates water balance through thirst and kidney function, but prolonged heat exposure without adequate hydration can lead to significant water deficits. This calculator estimates baseline TBW under normal conditions.

Not exactly. Total body water (TBW) is a structural measure of how much water exists in your body tissues — including inside cells, in blood plasma, and in interstitial fluid. Hydration status refers to whether your current fluid intake meets your body's needs. You can have a normal TBW estimate and still be temporarily dehydrated if you haven't consumed enough fluids.