Water intake calculator
Pick a group, see how much water a day is recommended.
How much water should I drink a day?
The National Academies set an adequate intake of about 3.7 liters of total water a day for men and 2.7 liters for women. About 3.0 L (13 cups) and 2.2 L (9 cups) of that comes from drinks, water included; the rest comes from food.
Does coffee or tea count?
Yes — the figures cover all beverages, not only plain water.
How much during pregnancy and breastfeeding?
About 3.0 liters of total water during pregnancy and 3.8 liters while breastfeeding, including 2.3 L and 3.1 L from drinks.
Is this a minimum?
No — these are adequate intakes, based on the typical intake of healthy people in the U.S., not minimum requirements. People who are very active or in hot weather may need more.
How many ounces is that?
A liter is 33.8 US fluid ounces, so 3.0 liters is about 101 fl oz and 2.2 liters about 74 fl oz.
How much of my water comes from food?
For adults the adequate intakes assume that food supplies roughly a fifth of total water: 0.7 L of the 3.7 L for men (19%) and 0.5 L of the 2.7 L for women (19%). Fruits, vegetables, soups and many other foods contain a lot of water, so a person who eats little of them may need to drink more.
Can you drink too much water?
Yes, although it is uncommon. Drinking very large amounts in a short time, faster than the kidneys can excrete it, can dilute the sodium in the blood (hyponatremia), which can be dangerous. The adequate intake figures are for a day, spread across the day. Follow the advice of your doctor if you have kidney, heart or other conditions that affect fluid balance.
What the numbers mean
The figures come from the National Academies of Sciences, Engineering, and Medicine (formerly the Institute of Medicine) report on dietary reference intakes for water, published in 2005. They are adequate intakes (AI): the amount judged enough for most healthy people, set from observed intake when there was not enough evidence to set a requirement. They are not a recommended dietary allowance and not a minimum. Total water means all beverages, including coffee and tea, plus the water in food. The page shows the total and the part from drinks, and converts the drinks figure to cups and fluid ounces.
Worked example: converting liters to cups and ounces
For an adult man the drink portion is 3.0 L. One liter is 33.8 US fluid ounces, so 3.0 L is 101 fl oz, which is 12.7 cups of 8 ounces. For an adult woman, 2.2 L is 74 fl oz, or 9.3 cups. Spread over waking hours, that is a glass of 8 ounces about every 1.7 hours for the woman's figure over a 16-hour day. In a refillable bottle of 16 fl oz, the man's drinks would be about 6.3 bottles.
What changes the need
Hot weather, hard exercise, and illness with fever, vomiting or diarrhea all raise the need for water, and the adequate intake figures are for healthy people under ordinary conditions. Pregnancy and breastfeeding have their own values, because the body also supplies the fetus or the milk. Medications such as diuretics change fluid balance, and a doctor should set the target for anyone taking them or managing a condition.
Common mistakes
Treating the number as a minimum, or as a goal to be reached by plain water alone, misreads the report: coffee, tea, milk, juice and food all count. Counting only the drinks figure against the total is the reverse error, and leads to overestimating how much to drink. Another is using the liters figure as if it were US quarts; a liter is slightly more than a quart. Finally, thirst and the color of urine are practical signals that no calculator can replace, and sudden changes in thirst can be a reason to see a doctor.
Sources: Institute of Medicine (now the National Academies), Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005): adequate intake of total water 3.7 L (men) and 2.7 L (women) a day, with the pregnancy and lactation values on this page; conversion factors from NIST SP 811. This page gives general information, not medical advice. Related: total body water calculator, calorie calculator and sleep calculator.
For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.