What is a normal body water percentage?

Typical ranges are 50–65% for males and 45–60% for females. Higher lean mass increases the percentage; higher body fat decreases it. These are general reference ranges—individual variation is normal.

Why does the Watson formula include age?

Body water content tends to decrease with age as lean mass decreases and body fat increases. The Watson formula accounts for this age-related decline, while the Hume-Weyers formula does not.

How accurate are these TBW formulas?

Both formulas were validated against isotope dilution (the gold standard). They provide reasonable estimates (±2–3 L) for most adults but may be less accurate for individuals with very high or very low body fat percentages.

What is the difference between intracellular and extracellular water?

Intracellular water (~⅔ of TBW) is inside your cells and is essential for cellular metabolism. Extracellular water (~⅓ of TBW) is outside cells—including blood plasma, lymph, and fluid between tissues.

Total Body Water Calculator

Name: Total Body Water Calculator
Author: Manish Kumar

Key Takeaways

Total body water typically comprises 50–65% of body weight in males and 45–60% in females.^[1]
Two established formulas—Watson (1980) and Hume-Weyers (1971)—provide estimates based on height, weight, and age.^[1]
~⅔ of body water is intracellular (inside cells) and ~⅓ is extracellular (blood plasma, interstitial fluid).^[2]
Body fat contains less water than lean tissue—higher body fat percentage results in lower water percentage.

Watson vs Hume-Weyers Formulas

The Watson formula (1980) includes age as a variable, reflecting the decrease in body water with aging. The Hume-Weyers formula (1971) uses only height and weight. Both are validated against isotope dilution methods, the gold standard for TBW measurement.^[1]

This calculator shows both results side-by-side so you can see how closely they agree. A large spread between the two may indicate that age-related changes are significant in your case. For body composition analysis, see our Body Roundness Index Calculator or FFMI Calculator.

Water Compartments

Body water is distributed between two main compartments. Intracellular water (~⅔ of TBW) is inside cells and essential for cellular function. Extracellular water (~⅓ of TBW) includes blood plasma, lymph, and interstitial fluid. The ratio remains relatively constant in most individuals.^[2]

How to Use This Calculator

Select your sex and enter your age, height, and weight.
Review both formula results and the average estimate.
Check the water compartment breakdown (intracellular vs extracellular).
Use the daily water reference as a general informational guideline.

Frequently Asked Questions

Sources & References

Total body water volumes for adult males and females estimated from simple anthropometric measurements. Watson PE, et al.. American Journal of Clinical Nutrition (1980)
Prediction of total body water and hydration. Hydration research review. European Journal of Clinical Nutrition (2023)

Manish Kumar

Certified Personal Trainer & Sports Nutritionist

NASM-CPTCertified Sports Nutritionist10+ Years Experience500+ Clients Coached

NASM-certified fitness and nutrition coach with over 10 years of hands-on experience helping people build strength, lose fat, and live healthier lives. Specializing in gym-based workouts with a strong focus on lifting technique, biomechanics, and practical exercise science. Through FitLifeRegime, sharing the tools, tips, and insights that have worked for hundreds of clients — helping you start your own fitness journey with confidence and clarity.

Learn more about Manish

NASM Certified

Certified Personal Trainer & Sports Nutritionist from the National Academy of Sports Medicine

Disclaimer: This tool is for informational and personal journaling purposes only. Results are estimates based on published formulas and may vary based on individual factors such as genetics, training history, and measurement technique.