Water Intake Calculator

Guide & FAQ

Guide: Water Intake Calculator

How the estimate works

There is no single correct amount of water. Needs rise with body size, activity, heat and some life stages. This calculator starts from body weight and adds simple adjustments, giving a practical daily target for drinks.

The formula

  • Base: 35 ml × body weight in kg
  • Exercise: + 350 ml for every 30 minutes
  • Climate: + 250 ml in warm weather, + 500 ml in hot or humid weather
  • Pregnancy: + 300 ml; breastfeeding: + 700 ml

Example: 70 kg gives 2,450 ml. Add 60 minutes of exercise (+700 ml) and hot weather (+500 ml) for 3,650 ml, about 3.7 litres or 123 fl oz.

Practical tips

  • Spread drinks across the day; the result is shown per waking hour and in 250 ml glasses.
  • Pale yellow urine is a simple hydration signal.
  • Coffee, tea, milk, juice and water-rich foods all count toward your fluid intake.
  • Drink more with fever, vomiting or diarrhoea, and at altitude.

Safety

This is a general guide for healthy adults, not medical advice. People with kidney, heart or liver conditions, or who are told to limit fluids, should follow their doctor. Very large amounts of water in a short time can be harmful. Use Copy result to save your target.

FAQ

How much water should I drink a day?

A common rule of thumb is about 30–35 ml per kg of body weight. This calculator uses 35 ml/kg and adds extra for exercise, heat and life stage.

Does the result include water from food?

No. It targets drinks. Food typically supplies about 20% of total water intake, so you may need a little less from drinks.

How is exercise counted?

About 350 ml (12 fl oz) is added for every 30 minutes of exercise to replace sweat. Long or intense workouts in heat need more.

Can I drink too much water?

Yes. Drinking far more than you need can dilute blood sodium (hyponatremia). Spread intake through the day and drink to thirst.

Who should not use this?

People with kidney, heart or liver disease, or on fluid restriction or diuretics, should follow their doctor’s advice. This is a general estimate only.