Water Intake Calculator
Most adults need about 2 to 3.7 litres of water a day in total, and roughly four fifths of it comes from drinks. Enter your details to see your range in litres and cups.
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- Updated 16 October 2026
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How much water a day
The lower number is EFSA's Adequate Intake, the higher one the National Academies'. Both are for a mild climate and moderate activity.
| Group | Total water a day | From drinks (about 80%) |
|---|---|---|
| Women | 2.0 to 2.7 L | 1.6 to 2.2 L |
| Men | 2.5 to 3.7 L | 2.0 to 3.0 L |
| Pregnant | 2.3 to 3.0 L | 1.8 to 2.4 L |
| Breastfeeding | 2.7 to 3.4 L | 2.2 to 2.7 L |
Older adults have the same values as younger adults in EFSA's opinion.
When you need more
- Exercise: you lose water as sweat, and how much varies a lot from person to person.
- Hot or humid weather: very active people in the heat can need 6 litres or more in total.
- Pregnancy and breastfeeding: about 0.3 and 0.7 litres more a day.
How we got it
Total water (drinks plus water in food) runs from the European Food Safety Authority's Adequate Intake (2.0 litres for women, 2.5 for men) to the US National Academies' (2.7 for women, 3.7 for men). EFSA adds 0.3 litres in pregnancy and 0.7 when breastfeeding. Both assume a mild climate and moderate activity. About 80% comes from drinks, as in the US survey data behind the National Academies values. For exercise we add 0.5 litres an hour, our rule of thumb; sweat losses vary a lot.
Updated . Sources: European Food Safety Authority, 2010, Dietary reference values for water; Institute of Medicine, 2005, Dietary Reference Intakes for Water.
The evidence
Every recommendation on this page links here. The badge shows what kind of source it is, so you can judge how strong it is.
- Guideline
Adequate total water intake (drinks of all kinds plus water in food) is 2.0 litres a day for women and 2.5 for men, in a moderate climate at moderate activity; 0.3 litres more in pregnancy and about 0.7 more when breastfeeding.
European Food Safety Authority, 2010, EFSA Journal 8(3):1459: Scientific Opinion on Dietary reference values for water
- Guideline
Adequate total water intake is about 3.7 litres a day for men and 2.7 for women, about 81% of it from drinks in US survey data. Thirst and drinking with meals keep most healthy people hydrated; very active people in hot weather can need 6 litres or more.
Institute of Medicine (National Academies), 2005, Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate: Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
Our own rules of thumb
These are our choices, not findings from a study. We list them so you know which parts are judgement calls.
- Drinks as 80% of the total.
- Adding 0.5 litres for each hour of exercise.
- Prefer not to say uses the midpoint of the male and female values.
- Cups of 240 ml.
Questions
How much water should I drink a day?
From drinks, about 1.6 to 2.2 litres for women and 2 to 3 litres for men in a mild climate, plus more when you exercise or it is hot. Food supplies the rest of your total.
Is 8 glasses a day right?
It is close for many people: 8 glasses of 250 ml is 2 litres, inside the range from drinks for most adults. There is no single number; the National Academies found that thirst and drinking with meals keep most healthy people well hydrated.
Should I drink half my body weight in ounces?
That rule is popular, but we found no guideline behind it. Official values are set by sex and life stage, not body weight, and go up with heat and exercise.
How much water should a woman drink a day?
About 1.6 to 2.2 litres a day from drinks, out of 2.0 to 2.7 litres in total, in a mild climate. Add about 0.3 litres when pregnant and 0.7 when breastfeeding.
How much water should a man drink a day?
About 2 to 3 litres a day from drinks, out of 2.5 to 3.7 litres in total, in a mild climate.
Do coffee and tea count?
Yes. The official values count water from drinks of all kinds and from food, not just plain water.
Turn this number into a plan
The free bodymaths app keeps your numbers, plans your training and meals around them, and adjusts as you log.
- A dated forecast that updates as you log
- Workouts and meals built around your numbers
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