Find a suggested daily water amount, based on your body weight.
A commonly cited 35ml-per-kg guideline.
Water: Weight (kg) × 35 ml
The water intake calculator suggests a daily amount of water based on body weight, using a common guideline of 35 millilitres per kilogram. Someone weighing 70 kg gets about 2.45 litres a day.
It is a starting point for people who are not sure whether they drink enough: office workers who forget to sip through the day, students during exams, older adults whose thirst signal is weaker, and anyone living through a hot Indian summer. The figure is a general guide for healthy adults. Needs rise with heat, exercise and illness, and fall somewhat for people who eat plenty of water-rich foods such as fruit, dal, curd and buttermilk.
1. Weigh yourself in kilograms.
2. Multiply by 35 to get millilitres per day: Water = Weight × 35 ml.
3. Divide by 1000 to convert to litres.
4. Add extra for hot weather and exercise, for example 400 to 800 ml for each hour of sweaty activity.
5. Spread the total across the day rather than drinking it all at once.
6. Use thirst and pale yellow urine as everyday checks that the amount suits you.
A larger body has more water in it and loses more through breath, skin and urine each day, so a per-kilogram guideline scales needs sensibly between a small and a large adult. The 35 ml per kg figure sits within the range commonly quoted for adults, roughly 30 to 40 ml per kg. It is an approximation built from average fluid turnover, not an exact physiological constant, which is why the calculator presents it as a suggestion.
Total water intake includes all beverages, such as tea, milk and buttermilk, and the water in food. Food commonly supplies around a fifth of daily water in many diets, and more in diets rich in fruit, vegetables, dal and rice. The body also makes a small amount of water by metabolising food. When comparing your intake with this calculator's figure, count all fluids, not just plain water, but remember that very salty or sugary drinks are poor substitutes.
Heat, humidity, physical work and exercise can raise needs well above the baseline, as can fever, vomiting or diarrhoea. On the other hand, people with some kidney, heart or liver conditions may be advised to limit fluids, and for them a weight-based rule can be wrong. If you have such a condition, follow your doctor's advice. Drinking very large amounts in a short time can also be harmful, so steady intake is better than forcing litres at once.
Sameer weighs 82 kg and works in an air-conditioned office in Mumbai, and wants a daily water target to fill his bottle against.
Answer: Suggested daily water intake 2.87 litres
Ignoring extra needs on hot days or after sport, especially in Indian summers.
Counting only plain water and forgetting tea, milk, buttermilk and water-rich foods.
Drinking the whole target in one sitting instead of spreading it through the day.
Applying the guideline despite a medical instruction to restrict fluids.
Setting a simple daily water target for work or study.
Planning hydration for long walks, treks or sports.
Helping older family members keep a regular intake.
Teaching body water balance in school biology or health classes.
Does this account for exercise or climate?
No. This is just a starting estimate. Hot weather, exercise, and being unwell all increase how much fluid you need, beyond this baseline.