Advanced Calculator
Enter physical data and choose a method. Results appear above this form after submission.
Formula Used
Watson Formula
Male:
TBW = 2.447 - 0.09156 × age + 0.1074 × height(cm) + 0.3362 × weight(kg)
Female:
TBW = -2.097 + 0.1069 × height(cm) + 0.2466 × weight(kg)
Hume Formula
Male:
TBW = 0.194786 × height(cm) + 0.296785 × weight(kg) - 14.012934
Female:
TBW = 0.34454 × height(cm) + 0.183809 × weight(kg) - 35.270121
Adjusted Percentage Method
TBW = body weight(kg) × adjusted water fraction
The base fraction changes with sex model, age, body type, and activity. The calculator limits it between 35% and 75% for practical safety.
Water Compartments
ICW = TBW × 2 / 3,
ECW = TBW × 1 / 3,
Plasma = ECW × 0.25,
Interstitial = ECW × 0.75
How to Use This Calculator
- Select the sex equation set that best matches the model you want.
- Enter age, height, and weight with correct units.
- Choose Watson, Hume, percentage, or average method.
- Select body type and activity for the percentage estimate.
- Add ambient temperature if you want a context note.
- Press the calculate button.
- Review total body water, body mass share, and compartment estimates.
- Use the CSV or PDF buttons to save the result.
Example Data Table
| Case | Age | Height | Weight | Method | Expected Pattern |
|---|---|---|---|---|---|
| Adult male | 35 | 178 cm | 80 kg | Average | Moderate to higher water volume |
| Adult female | 32 | 165 cm | 62 kg | Watson | Typical adult water share |
| Athletic user | 28 | 182 cm | 78 kg | Percentage | Higher fraction from lean mass |
| Older adult | 70 | 170 cm | 72 kg | Hume | Lower percentage than younger adults |
Understanding Total Body Water
Total body water is the water held inside and outside body cells. It is a large share of body mass. The share changes with age, sex, height, weight, muscle, fat, and training status. Physics treats this water as mass, volume, and distribution. One liter of water has nearly one kilogram of mass. That link makes the estimate useful for simple biophysical checks.
Why the Estimate Matters
Water affects density, heat transfer, blood volume, electrical conduction, and many transport processes. A higher lean mass usually means more body water. Fat tissue holds less water than muscle. Older adults often have a lower percentage. This calculator compares accepted equations and a percentage model. The comparison helps users see method spread instead of trusting one number blindly.
How Equations Behave
Watson and Hume equations use height, weight, age, and sex. They were built from population measurements. They work best for adults near common body ranges. The percentage method is easier. It uses a selected water fraction of body mass. It is useful for quick checks, teaching, and rough planning. The average option smooths the difference between models.
Reading the Output
The main result is shown in liters. The same amount is also shown as kilograms, pounds, and gallons. The chart separates intracellular water and extracellular water. Intracellular water is estimated as two thirds of total body water. Extracellular water is estimated as one third. Plasma and interstitial fluid are then split from the extracellular portion.
Practical Notes
This tool is for learning and estimation. It does not diagnose dehydration, edema, kidney problems, or electrolyte disorders. Real body water can change after exercise, illness, salt intake, pregnancy, or fluid treatment. Lab methods can give better values when accuracy matters. Use the result as a physics based estimate. Check unusual results with a qualified professional.
Design Limits
Equations are not perfect instruments. They are compact models. Extreme height, extreme weight, unusual muscle mass, and very young age can shift the estimate. That is why the page shows method comparison. A narrow spread suggests stable inputs. A wide spread suggests extra care. Review units before trusting any final value for best accuracy.
FAQs
1. What is total body water?
Total body water is the estimated volume of water inside and outside body cells. It includes intracellular fluid, extracellular fluid, plasma, and interstitial fluid.
2. Which formula should I choose?
The average method is useful for general comparison. Watson or Hume can be selected when you specifically want one published equation.
3. Is this a medical diagnosis tool?
No. It is an educational physics calculator. It estimates volume and distribution. It does not diagnose dehydration, edema, or illness.
4. Why does body type affect the percentage method?
Lean tissue holds more water than fat tissue. Athletic or lean users often have a higher water fraction than users with higher body fat.
5. Why are liters and kilograms similar here?
Water has a density close to one kilogram per liter. This makes liters and kilograms nearly equal for body water estimates.
6. What is intracellular water?
Intracellular water is water inside cells. A common estimate places it near two thirds of total body water.
7. What is extracellular water?
Extracellular water is water outside cells. It includes plasma and interstitial fluid. It is often estimated near one third of total body water.
8. Can exercise change the result?
The equation result may not change, but real body water can shift after sweating, drinking, salt intake, heat exposure, or intense activity.