Total Body Water

What is this formula?

The Total Body Water formula estimates the volume of water contained in the human body. It is commonly calculated as a fraction of body weight.

When to use it

Use this formula when estimating fluid compartments, calculating free water deficit, assessing hydration status, or performing pharmacokinetic calculations.

Example

Data:

BW = 70 kg

f = 0.60

Formula:

TBW = BW × f

Substitution:

TBW = 70 × 0.60

Result:

TBW = 42 L

The estimated total body water is 42 liters.

Applications

- Fluid balance calculations

- Nephrology

- Critical care medicine

- Pharmacokinetics

- Electrolyte disorder management

Note

This formula provides an estimate of total body water based on body weight and an assumed body water fraction. The value of f varies according to age, sex, obesity, and body composition. Alternative predictive equations such as Watson, Hume-Weyers, and anthropometric models may provide more accurate estimates in specific populations.