What it does
This calculator shows how much fluid a healthy adult needs a day, by two public guides side by side: the European Food Safety Authority (EFSA) and the US National Academies. Both give an “adequate intake” of total water, which counts food as well as drinks, so the page shows the part to drink, plus extra for exercise. A glasses counter tracks today.
These are estimates for healthy adults, not medical advice. If you also want a picture of your day, the sleep calculator and heart rate zones pages are good next steps.
How to use it
- Choose who it is for: woman, man, pregnant or breastfeeding.
- Type how many minutes you exercise today.
- Read the range from drinks, and the table row for each guide.
- Tap + Glass each time you finish a glass.
What each setting does
- Who: picks the adequate intake from each guide.
- Units: litres or US fluid ounces. The choice is not saved.
- Exercise today: minutes of activity that make you sweat.
- Extra per 30 min: the add-on for exercise, 0.5 L by default. A rule of thumb.
- Share from drinks: how much of the total comes from drinks. 80% is the usual figure; the rest comes from food.
- Glass size: for the glasses column and counter.
- Hot weather: shows a reminder to drink more. It does not change the numbers; needs in heat vary too much.
- Remember today’s count: off by default. When ticked, only today’s count is kept in this browser. Clear sets it to zero and deletes it.
Worked example
A man with no exercise: EFSA says 2.5 L of total water a day, and 80% of that is 2.0 L from drinks. The US guide says 3.7 L total, about 3.0 L from drinks. After 60 minutes of exercise, each figure goes up by 1.0 L, to 3.0 L and 4.0 L.
FAQs
Why do the two guides differ? They used different surveys. Your true need depends on size, activity and climate.
Do tea and coffee count? Yes, all drinks count, and so does water in food.
Can you drink too much? Yes. Very large amounts drunk quickly, such as in long endurance events, can be dangerous. Drink to thirst and follow your doctor’s advice if you have heart or kidney problems.
Where the numbers come from
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010), Scientific Opinion on Dietary Reference Values for water, EFSA Journal 8(3):1459: adequate total water intake 2.0 L women, 2.5 L men, +0.3 L pregnancy, +0.7 L breastfeeding (checked 2026-11-10).
- Institute of Medicine, US National Academies (2004), Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate: adequate total water 2.7 L women, 3.7 L men, 3.0 L pregnancy, 3.8 L breastfeeding; about 80% from drinks (checked 2026-11-10).
- American College of Sports Medicine (2007), position stand on exercise and fluid replacement: sweat losses vary widely, so the 0.5 L per 30 minutes add-on is a rule of thumb and editable.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.