Water is the primary component of human life, accounting for the majority of your body mass. Maintaining the right fluid balance supports metabolic processes, regulates temperature, lubricates joints, and keeps organs functioning smoothly. Monitoring total body water helps athletes, medical professionals, and health-conscious individuals gauge hydration and detect potential imbalances. This calculator uses a scientific approach to estimate water volume and its percentage of your total weight.
Researchers developed various formulas to approximate total body water (TBW) based on physical characteristics. One well-known method is the Watson formula. Expressed in MathML, the equations are:
For adult males the coefficients are a = 2.447, b = 0.3362, c = 0.1074, and d = −0.09516. For adult females they are a = −2.097, b = 0.2466, c = 0.1069, and d = 0. This formula returns TBW in liters when weight W is in kilograms, height H in centimeters, and age A in years.
The calculation requires your age, gender, height, and weight. Age matters because body composition shifts over time—older adults often lose muscle mass and gain fat, which contains less water. Height and weight help approximate the overall volume of your body, and gender recognizes differences in average muscle-to-fat ratios. Although the formula can't account for every individual nuance, it offers a reliable starting point for most healthy adults.
While water makes up roughly 60 % of an adult male's body and 50 %–55 % of an adult female's, the exact value varies depending on lifestyle, fitness level, and even climate. The table below provides broad averages across age groups:
| Age Range | Male (%) | Female (%) |
|---|---|---|
| 18–30 | 59–63 | 50–55 |
| 31–50 | 55–60 | 47–52 |
| 51+ | 52–56 | 45–50 |
Simply enter your personal data and press the Calculate button. The script converts the Watson formula into JavaScript to compute total body water in liters. It then divides that number by your weight to determine the percentage of your body composed of water. Because calculations occur entirely in your browser, your information stays private and the page works offline after loading.
Imagine a 35-year-old female, 165 cm tall and weighing 60 kg. Plugging these values into the formula yields:
The result is about 31 L. Dividing by the weight gives a body water percentage of roughly 52 %. This falls within the typical range for adult women. Repeating the calculation with your own data lets you track fluctuations over time or after changes in diet and exercise.
Athletes often monitor body water because even slight dehydration can reduce endurance, strength, and cognitive function. By knowing your baseline, you can better judge how much fluid to replace during intense workouts or hot weather. Some smart scales and fitness trackers attempt to estimate body water using bioelectrical impedance, but the Watson formula offers a quick alternative when such tools aren't available.
No single equation perfectly represents the complexities of human physiology. The Watson formula works best for healthy adults between 18 and 60 years old. It may be less accurate for children, elderly individuals, pregnant women, or people with certain medical conditions. Factors like extreme obesity, very low body fat, or unusual muscle mass can also skew the results. Still, for most users it provides a useful approximation.
If your calculated body water percentage falls within the typical range shown earlier, you're likely well hydrated. A significantly lower value might suggest dehydration or high body fat content. Remember that sudden changes, such as after a workout or a long flight, can temporarily alter your water balance. Drinking water and eating foods with high moisture content helps restore equilibrium.
Developing healthy hydration habits is easier when you understand your body's water needs. Carry a refillable bottle and sip throughout the day. Increase intake during hot weather or strenuous exercise. Many people benefit from starting the morning with a glass of water and drinking before every meal. Fruits and vegetables contribute to your total intake too, so include them in your diet.
Health professionals sometimes use total body water to estimate dosing for certain medications or to monitor fluid balance in hospital settings. Athletes track changes in hydration level as they adjust training routines. Casual users might check their percentage after adopting a new workout program or diet. Because the calculator runs locally, you can revisit it often and keep a personal record of your results.
Repeat measurements under similar conditions—such as first thing in the morning—to see how your body water fluctuates. If you notice a consistent downward trend, you may need to increase daily fluid intake. Conversely, a sudden spike might indicate water retention, which can result from high-sodium meals or certain medications. Observing these patterns can guide conversations with healthcare professionals.
Your body relies on adequate water to function properly. This calculator empowers you to estimate total body water and evaluate it as a percentage of your weight. While the Watson formula offers a solid approximation for most adults, remember that it's only one piece of the hydration puzzle. Listen to your body's thirst cues, pay attention to urine color, and consult a healthcare provider if you're concerned about fluid balance. By combining these strategies, you can maintain healthy hydration and support overall well-being.
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