Water Intake Calculator
A rough daily water estimate based on your weight and exercise.
Good to know. Food provides a fair share of the water you need. You don’t have to drink all of it.
Not medical advice. A general estimate for healthy adults.
How it works
In plain words
A common rule of thumb is 30–35 millilitres of water per kilogram of body weight each day, plus about half a litre for every hour of exercise. We show the middle of that range.
The formula
base = weight (kg) × 0.030 to 0.035 L exercise = minutes ÷ 60 × 0.5 L estimate = midpoint of base + exercise
Worked example
At 70 kg with 30 minutes of exercise: 2.1–2.45 L as a base, plus 0.25 L for exercise, gives about 2.5 L a day.
Sources
- EFSA, Scientific Opinion on Dietary Reference Values for water, 2010 About 2.0 litres a day for women and 2.5 for men, from all drinks and food.
Sources checked September 29, 2026. 5 automated tests check its answers on every change.
About the water intake calculator
There is no single right amount of water for everyone. What you need depends on your size, how active you are, the weather, what you eat, and your health. This calculator gives a reasonable starting estimate using a widely used rule of thumb: 30 to 35 millilitres per kilogram of body weight, plus extra for exercise.
The total includes all water, not just plain water. Tea, coffee, milk, juice and water-rich foods like fruit, vegetables and soup all count. Food typically provides around 20% of the water most people take in. The European Food Safety Authority’s reference values are about 2.0 litres a day in total for women and 2.5 litres for men, which is in the same range as this estimate for many people.
Your body is good at telling you when you need more. Thirst, and urine that is dark yellow, are signs to drink more. Pale straw-coloured urine usually means you are drinking enough. You will need more in hot weather, at altitude, when you are ill with a fever or vomiting, and when pregnant or breastfeeding.
Drinking far more than you need is not better, and can be dangerous in extreme cases. If you have heart or kidney problems, follow your doctor’s advice on fluids, which may be quite different.
Questions people ask
How much water should I drink a day?
A common guide is 30–35 ml per kg of body weight, more if you exercise or it is hot. For a 70 kg adult that is roughly 2 to 2.5 litres from all sources.
Do tea and coffee count?
Yes. They count towards your fluid intake. Their mild diuretic effect does not cancel out the water they contain.
Is the "8 glasses a day" rule right?
It is a rough, easy-to-remember guide, not a scientific rule. Needs vary with size, activity and climate.