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Body Water Calculator

Estimate total body water from adult age, height and weight using a published anthropometric equation. See the estimate in litres and as a share of entered body mass.

Estimate only; it does not measure hydration or tell you how much to drink. Watson’s 1980 adult equations use male/female categories from their source data and may not fit every person or population. Not for minors, pregnancy, dialysis, edema, diagnosis or clinical decisions. For health questions, ask a qualified clinician.

Watson et al. (1980): male = 2.447 − 0.09516 × age + 0.1074 × height(cm) + 0.3362 × weight(kg); female = −2.097 + 0.1069 × height(cm) + 0.2466 × weight(kg). The percentage treats 1 L of water as approximately 1 kg.

How is total body water estimated?

Choose one of the Watson equation variants, enter adult age, height and weight, then calculate. The result is a population-based estimate, not a direct measurement.

Frequently asked questions

How is total body water estimated?

Choose one of the Watson equation variants, enter adult age, height and weight, then calculate. The result is a population-based estimate, not a direct measurement.

Are my measurements uploaded?

No. The calculation runs locally in this browser and the values are not uploaded or saved by this tool.

Is this a hydration or dehydration test?

No. It estimates total body water from a population equation. It cannot measure hydration status or diagnose dehydration.

What does the percentage mean?

It is estimated litres divided by the entered body mass, treating 1 litre of water as about 1 kilogram. It is not a target or a healthy-range score.

Who should not use this estimate for decisions?

It is not intended for children, pregnancy, dialysis, edema or clinical decisions. A clinician can assess individual health context and direct measurements.