Water Intake Calculator
How much water should you drink a day? Pick your group and weight to compare the official adequate intakes from the US and Europe with a simple body-weight goal.
How much water should you drink a day?
There is no single number that fits everyone. Health authorities publish an adequate intake: the amount that healthy, well-hydrated people typically take in. It covers total water – plain water, every other drink and the water in food.
| Group | US total water | US from drinks | EFSA total water |
|---|---|---|---|
| Woman (19+) | 2.7 L | 2.2 L | 2.0 L |
| Man (19+) | 3.7 L | 3.0 L | 2.5 L |
| Pregnant | 3.0 L | 2.3 L | 2.3 L |
| Breastfeeding | 3.8 L | 3.1 L | 2.7 L |
| Girl (14–18) | 2.3 L | 1.8 L | 2.0 L |
| Boy (14–18) | 3.3 L | 2.6 L | 2.5 L |
The US National Academies set 2.7 L a day for women and 3.7 L for men, the same for every adult age from 19 to over 70. About 2.2 L (9.3 cups, 74 fl oz) and 3.0 L (12.7 cups, 101 fl oz) of that comes from drinks. The European Food Safety Authority (EFSA) sets 2.0 L for women and 2.5 L for men at moderate temperatures and activity; from age 14 the adult values apply, older adults included. Pregnancy adds 300 ml and breastfeeding about 700 ml.
Why the US and European numbers differ
The US figures are the median total water intake in US survey data. EFSA combined observed intakes with the amount needed for a desirable urine concentration. Neither is a minimum you must hit: both are reference values for groups of healthy people, and the US panel said it offers no rule of thumb based on how many glasses to drink.
About 80% comes from drinks
In the US data, about 80% of total water came from drinking water and other beverages and about 20% from food. Coffee and tea count too: the report says caffeinated drinks contribute as much as non-caffeinated ones.
Water by body weight (rule of thumb)
Many apps scale water to body weight with 30 ml per kilogram (about 0.46 fl oz per pound). It is not an official recommendation – neither EFSA nor the US Academies scale adult intake by weight – but it makes a reasonable personal goal.
| Weight | 30 ml/kg | fl oz |
|---|---|---|
| 110 lb (50 kg) | 1.5 L | 51 |
| 130 lb (59 kg) | 1.75 L | 59 |
| 150 lb (68 kg) | 2.05 L | 69 |
| 170 lb (77 kg) | 2.3 L | 78 |
| 190 lb (86 kg) | 2.6 L | 88 |
| 220 lb (100 kg) | 3.0 L | 101 |
When you need more, or less
- Heat and hard exercise raise losses. EFSA notes they can reach about 8 litres a day in extreme conditions and must be replaced along with electrolytes.
- For most healthy people, thirst is a good guide.
- Drinking huge amounts quickly is dangerous too: the kidneys can pass at most about one litre an hour.
- If you have kidney or heart disease and were told to limit fluids, follow your doctor's advice.
Sources
- Institute of Medicine (US National Academies), Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, chapter 4: Water (2005)
- National Academies news release: Report sets dietary intake levels for water, salt and potassium (February 11, 2004)
- EFSA Panel on Dietetic Products, Nutrition and Allergies, Scientific Opinion on Dietary reference values for water (EFSA Journal 2010;8(3):1459)
- EFSA, Dietary Reference Values for nutrients: Summary report (2017)
Frequently asked questions
How much water should I drink a day?
The US National Academies set an adequate intake of 2.7 L of total water a day for women and 3.7 L for men, counting water in food. About 2.2 L (9.3 cups) and 3.0 L (12.7 cups) of that comes from drinks. EFSA's figures are 2.0 L and 2.5 L.
Do I really need 8 glasses of water a day?
Not as a rule. The National Academies said they offer no rule of thumb for how many glasses to drink; most healthy people meet their needs by letting thirst guide them, and every drink counts, coffee and tea included.
How much water should I drink based on my weight?
A common rule of thumb is 30 ml per kg (about 0.46 fl oz per pound). At 150 lb that is about 2.05 L or 69 fl oz. It's a personal goal, not an official value.
Does food count toward water intake?
Yes. In the US survey data about 20% of total water came from food and about 80% from drinks.
How much more water when pregnant or breastfeeding?
The US values are 3.0 L of total water a day in pregnancy and 3.8 L when breastfeeding. EFSA adds 300 ml and about 700 ml to the 2.0 L for women.
Can you drink too much water?
Yes. The kidneys can pass at most about a litre of urine an hour, and drinking far more than that in a short time can dilute the blood's sodium dangerously (water intoxication).