Total Body Water Calculator (Watson Formula)
Litres of water in your body from sex, age, height and weight, by the Watson equations, and the fat-free and fat mass that implies.
Results
What this tool does
Water makes up roughly half to two thirds of an adult's weight, and most of it sits in muscle, not fat, which is why women and older people carry a smaller share. Patricia Watson and colleagues published these equations in the American Journal of Clinical Nutrition in 1980, fitted to dilution measurements, and they are still used to estimate how alcohol or some drugs spread through the body. Dividing by 0.732, the water content of fat-free tissue measured by Pace and Rathbun in 1945, turns the result into a body composition estimate. It describes the average person with your measurements; daily swings in hydration, a meal or a hard workout are not captured.
Formula
men: TBW = 2.447 − 0.09516 age + 0.1074 H + 0.3362 W · women: TBW = −2.097 + 0.1069 H + 0.2466 W
Variables
| Symbol | Meaning | Unit |
|---|---|---|
sx | Sex | — |
ag | Age | a |
ht | Height | cm |
w | Weight | kg |
TB | Total body water | L |
PC | Share of body weight | % |
FF | Fat-free mass implied (73.2 % water) | kg |
FM | Fat mass implied | kg |
Worked example
- Sex1
- Age40 a
- Height175 cm
- Weight75 kg
- Total body water42.7 L
- Share of body weight56.9 %
- Fat-free mass implied (73.2 % water)58.3 kg
- Fat mass implied16.7 kg
Limitations
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.