Body Water Calculator
Estimate your body water percentage using the Watson Formula
Track your body composition over time with Progress
What is body water percentage?
Body water percentage is the proportion of your total weight that is made up of water. Water is in your blood, your organs, your muscles, and even your bones. It keeps everything running, from circulation and digestion to temperature regulation.
The amount of water in your body changes a little every day. Muscle holds more water than fat, so people with more muscle mass tend to sit slightly higher. Hydration, hormones, and even the weather all play a part.
Track your body composition alongside your measurements with Progress.
Your body is more than one number
Body water is a useful piece of the picture, but it is just one piece. When you track it alongside your weight, body measurements, and how you feel, you get a much clearer sense of what is actually changing over time.
How the Watson Formula works
The Watson Formula was developed in 1980 to estimate total body water (TBW) in litres using simple measurements. There are separate equations for men and women because body composition differs.
For men, the formula uses age, height, and weight. For women, it uses height and weight. Once you have your total body water, dividing it by your weight gives you your body water percentage.
It is not as precise as clinical methods like bioelectrical impedance, but it gives a reliable estimate for most healthy adults and works well for spotting trends over time.
Body water percentage ranges
These are typical healthy ranges for adults. They are general guidelines, not strict rules. Athletes and people with more muscle mass often sit slightly higher.
| Group | Healthy Range | What It Means |
|---|---|---|
| Adult men | 50 – 65% | A typical range, often higher in athletes |
| Adult women | 45 – 60% | A typical range, often higher in athletes |
| Below range | Lower than typical | Could suggest dehydration or higher body fat |
| Above range | Higher than typical | Common in athletes, sometimes linked to water retention |
Body water percentage is an estimate. For a fuller picture, track it over time alongside other metrics like weight, body measurements, and how you feel.
Tips for staying hydrated
Hydration affects how you feel, how you train, and even how you sleep. A few simple habits go a long way.
- Start the day with a glass of water before coffee or tea
- Keep a water bottle within reach during the day
- Drink a little extra around workouts and on hot days
- Include water-rich foods like fruit, vegetables, and soups
- Check the colour of your urine. Pale yellow is a good sign
If you have a medical condition that affects fluid balance, follow the advice your doctor has given you rather than a general rule of thumb.
Frequently Asked Questions
What is the Watson Formula?
The Watson Formula estimates your total body water (TBW) in litres using your age, height, and weight. There are separate equations for men and women to account for differences in body composition. It was developed in 1980 by Watson and colleagues as a practical way to estimate body water without specialised equipment.
What is a healthy body water percentage?
A typical healthy range is 50 to 65% for men and 45 to 60% for women. These ranges vary with age, body composition, and hydration. Athletes often sit slightly higher because muscle holds more water than fat. The trend over time tells you more than any single reading.
How accurate is the Watson Formula?
The Watson Formula gives a reasonable estimate for most healthy adults, but it is not as precise as clinical methods like bioelectrical impedance or isotope dilution. It works best for tracking trends over time, especially when you measure consistently at the same time of day.
Should I track body water percentage?
For most people, body water percentage is helpful background information rather than a key metric. It can be useful if you are training hard, watching your hydration, or your doctor has asked you to monitor it. Body measurements, weight, and how you feel will usually tell you more day to day.
Why does body water percentage change?
Body water naturally fluctuates with hydration, food and salt intake, exercise, hormones, and the weather. It also tends to be slightly higher in people with more muscle mass and slightly lower with more body fat. Small day-to-day changes are completely normal.
Track your body composition over time with Progress