Total Body Water Calculator
Estimate your total body water (TBW) in litres using the Watson formula. Enter your sex, age, height, and weight to see how many litres of water your body holds and what share of your weight that is.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
- Population estimate; daily hydration fluctuates.
Formula
Male TBW = 2.447 − 0.09516 × age + 0.1074 × height(cm) + 0.3362 × weight(kg); Female TBW = −2.097 + 0.1069 × height + 0.2466 × weight
- The Watson formula estimates total body water from sex, age, height, and weight — the most widely used clinical equation.
- Age only affects the male equation; the female equation depends on height and weight.
- Water typically makes up about 50–65% of body weight, varying with body fat (fat holds less water than muscle).
- Results are population estimates and shift through the day with food, drink, and activity.
- For medical fluid management, rely on direct measurement rather than a formula.
Man, 30, 175 cm, 75 kg
Inputs
- Gender: male
- Age: 30 years
- Height: 175 cm
- Weight: 75 kg
TBW = 2.447 − 0.09516×30 + 0.1074×175 + 0.3362×75 ≈ 43.5 L, about 58% of body weight.
Frequently asked questions
What is total body water?
It is the total volume of water in your body — inside and outside your cells — usually expressed in litres or as a percentage of body weight.
How does the Watson formula work?
It estimates total body water from your sex, age, height, and weight using equations derived from measured body water data.
What is a normal body water percentage?
Roughly 50–65% of body weight, higher in men and leaner people because muscle holds more water than fat.
Why does body water change?
It rises and falls with hydration, meals, exercise, and sweat, so a single reading is just a snapshot.
How accurate is this estimate?
The Watson formula is a good population estimate but not a substitute for direct measurement when clinical accuracy is needed.
Related calculators
Body Water Percentage Calculator Estimate your body water percentage — the share of your weight made up of water — using the Watson total body water formula. Enter your sex, age, height, and weight to see your body water percentage and total body water in litres. Body Fat Calculator Popular Estimate your body fat percentage with the US Navy circumference method. Enter your sex, height, and a few tape measurements to see your body fat percentage, category, and healthy range. Lean Body Mass Calculator Lean Body Mass Calculator is a health and wellness calculator that helps you calculate lean body mass values from your input data. The formula used is: Boer (men): LBM = 0.407 × weight + 0.267 × height(cm) − 19.2\nBoer (women): LBM = 0.252 × weight + 0.473 × height(cm) − 48.3\nHume (men): LBM = 0.3281 × weight + 0.3393 × height(cm) − 29.534\nHume (women): LBM = 0.29569 × weight + 0.41813 × height(cm) − 43.293. Enter values using the units shown next to each input field (e.g. kg, cm, years).