How much water should I drink?
- Enter your body weight in kilograms or pounds.
- Set how many minutes you exercise on a typical day.
- Tick hot weather if you live somewhere warm or work outside, and choose pregnancy or breastfeeding if they apply.
- Read your daily target in litres or ounces, and as 250 ml (8 oz) glasses.
How the estimate works
The calculator starts from about 33 ml of drinks per kilogram of body weight, which puts an average 70 kg adult at around 2.3 litres a day. That lines up with the European Food Safety Authority's reference values of 2.0 litres total water a day for women and 2.5 litres for men, about 80% of which comes from drinks and the rest from food. It then adds roughly 350 ml for every 30 minutes of exercise to replace sweat, 500 ml in hot or humid weather, and the extra fluid recommended during pregnancy (300 ml) and breastfeeding (700 ml).
All drinks count, including tea, coffee and milk; caffeine's mild diuretic effect is smaller than the water in the cup. The simplest check is the colour of your urine: pale straw means you are well hydrated, dark yellow means drink more. Drinking far more than you need is rarely harmful for healthy people, but very large amounts in a short time, especially during endurance events, can be dangerous.
The result is calculated in your browser; nothing is saved or sent.
Is "8 glasses a day" right?
It is a reasonable rule of thumb for many adults, but needs vary with size, activity and climate, which is what this calculator accounts for.
Does coffee count towards water intake?
Yes. Moderate amounts of coffee and tea hydrate you almost as well as water.
Can I drink too much water?
Yes, in rare cases. Drinking several litres in a few hours can dilute blood sodium (hyponatraemia). Spread intake through the day.