Body Water Percentage Calculator

Total body water (TBW) represents the total amount of water in the human body, expressed as a percentage of total body weight. Water is essential for virtually every bodily function including temperature regulation, nutrient transport, waste elimination, and cellular processes.

The Watson Formula: This calculator uses the Watson formula, one of the most widely validated equations for estimating total body water:

For males: TBW (liters) = 2.447 - 0.09156 × age + 0.1074 × height(cm) + 0.3362 × weight(kg)

For females: TBW (liters) = -2.097 + 0.1069 × height(cm) + 0.2466 × weight(kg)

The percentage is then calculated as: Body Water % = (TBW in liters / weight in kg) × 100

Normal body water percentages:

• Adult males: 50-65% of body weight
• Adult females: 45-60% of body weight
• Infants: About 75% of body weight
• Elderly adults: 45-55% of body weight

Women generally have a lower body water percentage than men because they typically have a higher proportion of body fat, and fat tissue contains less water than muscle tissue.

Why body water percentage matters: Maintaining proper hydration is critical for health. Even mild dehydration of 1-2% body water loss can impair cognitive function, physical performance, and mood. Severe dehydration (losing more than 5% of body water) can be medically dangerous.

Factors affecting body water:

• Body composition: Muscle tissue is about 75% water, while fat tissue is only about 10% water
• Age: Body water percentage decreases with age as muscle mass typically declines
• Physical activity: Athletes with more muscle mass tend to have higher body water percentages
• Climate and altitude: Hot climates and high altitude increase water loss through sweat and respiration

Daily water intake recommendation: A general guideline is to consume about 30-35 ml of water per kilogram of body weight per day. Active individuals and those in hot climates need more. The actual amount varies based on diet, activity level, and environmental conditions.