Total Body Water Calculator
Estimate your total body water (TBW) using the widely used Watson formula, based on your sex, age, height, and weight.
What is total body water?
Total body water (TBW) is the estimated amount of water contained in your body, spread across blood, cells, and the fluid between cells. It typically makes up somewhere between 45% and 65% of total body weight, depending on sex, age, and body composition.
The Watson formula
This calculator uses the Watson formula (1980), one of the most widely referenced equations for estimating TBW from simple measurements:
- Men: TBW = 2.447 − (0.09145 × age) + (0.1074 × height in cm) + (0.3362 × weight in kg)
- Women: TBW = −2.097 + (0.1069 × height in cm) + (0.2466 × weight in kg)
This is a population-based estimate, not a direct measurement. Actual body water varies with hydration status, muscle mass, and health conditions. This tool is for general educational purposes and is not a substitute for clinical assessment.