Daily Water Intake Estimator
A rough guide to daily fluid needs based on body weight, activity and climate.
Formula
roughly 30–35 ml per kg of body weight, adjusted for activity and heat
Tips
- Thirst is a good guide for most healthy adults. Pale straw-coloured urine is a more useful signal than hitting a numeric target.
- Around a fifth of typical fluid intake comes from food. Tea, coffee and juice all count towards the total — the idea that caffeine dehydrates at normal intakes is not supported by the evidence.
- Needs rise with exercise, heat, altitude, fever, pregnancy and breastfeeding, and fall in cold weather.
- Drinking far beyond thirst is not benign. Consuming several litres in a short period can dilute blood sodium dangerously, which is a genuine medical emergency.
- Kidney disease, heart failure and some medications change fluid requirements substantially. If any apply, follow your clinician’s advice rather than a general formula.
Frequently asked questions
Is eight glasses a day correct?
It is a memorable rule with no strong evidence behind it. Actual needs vary with body size, activity, climate and diet, which is why this shows a range rather than a single figure. For most healthy people, drinking to thirst works.