Estimate your body water volume and percentage with the Watson equation.
Estimated body water
—Enter your measurements
Where body water is found
Illustrative split, not measured compartments.
Understanding your estimate
- Water is distributed throughout body tissues.
- Lean tissue contains more water than fat.
- This estimate does not measure today’s hydration.
Text summary · PDF in member tools
Step-by-step calculation
The Watson calculation
Total body water is estimated from adult anthropometric measurements.
Water mass is approximated as 1 kg per liter when expressing the result as a share of body weight.
Frequently asked questions
What does total body water mean?
Total body water is the water in all body tissues, including fluid inside and outside cells. Watson estimates this volume from adult anthropometric measurements. It is not a direct measurement.
Can this diagnose dehydration?
No. A predicted body-water percentage cannot diagnose dehydration or fluid overload. The result depends on body size, age and sex, and does not measure current fluid balance. Do not use this estimate as a drinking-water target or to adjust treatment.
Why does biological sex affect the formula?
Watson derived separate adult male and female equations. The original male equation includes age; the female equation uses height and weight only. These categories describe the source model and may not represent every person’s body composition.
Are cell-fluid values measured?
No. Intracellular water is illustrated as about two-thirds of total body water and extracellular water as about one-third. Actual proportions vary. These outputs are an educational allocation of the estimate, not a patient-specific measurement.
Who is this calculator intended for?
The Watson equations were developed for adults. This tool is not a pediatric, pregnancy, edema or dialysis assessment. Body composition and population differences can affect individual accuracy. Seek a qualified clinician’s assessment for fluid-balance concerns.
What does the Total Body Water calculate?
Estimate your body water volume and percentage with the Watson equation.
Which values should I enter?
Choose the biological-sex equation and enter adult age, height and weight. Select cm or inches and kg or pounds. You do not need to know total body water beforehand.
What formula does this calculator use?
It uses the original Watson adult equations. The male age coefficient is 0.09516; the female equation has no age term. Height is converted to cm and weight to kg before calculation.
Why might my result differ from another source?
Check the equation, age coefficient and units. This tool uses 0.09516 in the male Watson equation and rounds only displayed results. Individual body composition and population differences limit accuracy.
Does the result update automatically?
Yes. Changing a measurement or the biological-sex selection recalculates the result and charts. Unit switches preserve the underlying measurements. Invalid entries clear the previous result.
Sources & references
References inform the content; no institutional endorsement.
