Total Body Water Calculator

This calculator relies on the Watson formula, a widely accepted anthropometric regression equation used to estimate total body water (TBW) in liters. For males, the calculation is defined as: TBW = 2.447 - (0.09156 * age) + (0.1074 * height in cm) + (0.3362 * weight in kg). For females, the formula adjusts for physiological body composition differences: TBW = -2.097 + (0.1069 * height in cm) + (0.2466 * weight in kg). Once the absolute water weight in liters is determined, your total body water percentage is calculated by dividing the TBW by your total body weight and multiplying by 100.

Consider a 35-year-old male who stands 175 cm tall and weighs 70 kg. To find his total body water using the male Watson equation, we substitute the variables into the formula: TBW = 2.447 - (0.09156 * 35) + (0.1074 * 175) + (0.3362 * 70). This breaks down to 2.447 - 3.2046 + 18.795 + 23.534, which yields approximately 41.57 liters of total body water. To find his body water percentage, we divide this volume in kilograms (assuming 1 liter of water equals 1 kg) by his total body weight: (41.57 / 70) * 100 = 59.4%. This indicates a healthy hydration level within the typical male range of 50 to 60 percent.

For the most consistent results, always weigh yourself under the same conditions, preferably in the morning after fasting and using the restroom. Keep in mind that predictive equations offer strong estimations but cannot replace advanced clinical methods like bioelectrical impedance or deuterium dilution. Additionally, remember that daily fluctuations in sodium intake, carbohydrate storage, and intense exercise can temporarily alter your total body water readings.