Body Water Calculator

Body water percentage is the proportion of your total body weight that is water. Water is essential for every bodily function — regulating temperature, transporting nutrients, flushing waste, lubricating joints, and facilitating chemical reactions. Total body water (TBW) includes water inside cells (intracellular) and outside cells (extracellular, including blood plasma and interstitial fluid).

Normal ranges vary by sex and age: Adult men: 50–65% (average ~60%). Adult women: 45–60% (average ~50%). Infants: 75–78% (higher due to less body fat). Elderly adults: 45–55% (TBW decreases with age). Athletes may have higher percentages (65–70%) due to greater muscle mass. Women naturally have lower TBW due to higher average body fat percentage.

This calculator uses the Watson Formula (1980), one of the most validated formulas for estimating TBW from anthropometric measurements. Men: TBW (L) = 2.447 − (0.09156 × age) + (0.1074 × height_cm) + (0.3362 × weight_kg). Women: TBW (L) = −2.097 + (0.1069 × height_cm) + (0.2466 × weight_kg). The result is expressed in litres and as a percentage of body weight.

Drink adequate water (2–3 litres/day for adults, more in hot weather or during exercise). Eat water-rich foods (cucumbers 96%, watermelon 92%, oranges 86%). Reduce alcohol and caffeine consumption. Increase muscle mass through strength training (muscle holds more water than fat). Avoid excessive sodium which causes water retention in the wrong compartments.

Mild (1–2% loss): thirst, darker urine, mild fatigue. Moderate (3–4% loss): headache, reduced physical performance, dry mouth, dizziness. Severe (5%+ loss): rapid heartbeat, confusion, muscle cramps, significantly reduced urine output. Chronic mild dehydration affects cognitive performance, kidney function, and digestion without obvious acute symptoms.

Yes. TBW decreases progressively with age: Infants (~75%) → Young adults (~60% men, ~50% women) → Elderly (~52% men, ~46% women). This decline is primarily due to: increased body fat percentage (fat contains very little water vs muscle which is ~73% water), reduced kidney function, and decreased thirst sensation in older adults.

Men naturally have higher muscle mass and lower body fat than women of similar size. Muscle tissue is approximately 73% water while fat tissue is only 10–15% water. Since men typically have more muscle (higher lean body mass), their total body water percentage is higher. Hormonal differences (estrogen promotes fat storage) also contribute to this sex difference.

Yes. Total body water (TBW) is the total amount of water in your body at any given time. Daily water intake is the amount you need to consume each day to maintain that level. You lose water constantly through urine, sweat, breathing, and feces — roughly 2–3 litres/day in a sedentary adult in a temperate climate. Your daily intake must replace these losses.