Water Intake Calculator
This water intake calculator shows how much total water adults typically need each day, based on the National Academies' adequate intakes for men, women, pregnancy and breastfeeding. Results are in liters, cups and fluid ounces.
Result
About 11.4 cups (2.7 L) of water a day
| Total water (food + drinks) | 2.7 L · 91 fl oz |
|---|---|
| From drinks (≈80%) | 2.2 L · 9.1 cups |
| From food (≈20%) | 0.5 L |
National Academies adequate intakes: a population average for healthy adults, not a personal requirement.
How Much Water Do Adults Need?
In 2004, the National Academies (then the Institute of Medicine) set adequate intakes (AI) for water. An AI is the average daily amount that healthy people typically consume when they’re well hydrated. It’s a guide for groups of people, not a precise personal requirement.
The figures are for total water: everything you drink plus the water in food.
Adequate Intake of Total Water (Adults 19+)
| Group | Liters/day | US cups/day | Fluid ounces/day |
|---|---|---|---|
| Men | 3.7 | 15.6 | 125 |
| Women | 2.7 | 11.4 | 91 |
| Pregnancy | 3.0 | 12.7 | 101 |
| Breastfeeding | 3.8 | 16.1 | 128 |
How the Calculator Works Out Cups and Drinks
Cups = liters ÷ 0.2366 (one US cup is 8 fl oz, or about 236.6 mL)
Fluid ounces = liters ÷ 0.02957
The report notes that about 80% of total water typically comes from drinks and 20% from food:
From drinks ≈ total water × 0.8
Worked example: adult woman
- Total water: 2.7 L
- In cups: 2.7 ÷ 0.2366 = 11.4 cups
- In fluid ounces: 2.7 ÷ 0.02957 = 91 fl oz
- From drinks: 2.7 × 0.8 = 2.16 L, about 9.1 cups
- From food: 2.7 − 2.16 = 0.54 L
For an adult man, the same steps give 3.7 L of total water, of which about 2.96 L (12.5 cups) from drinks.
Tips and Limitations
All drinks count
The adequate intakes include water from every beverage, not only plain water. Milk, juice, tea and coffee all contribute.
Needs change day to day
Physical activity and climate change how much water the body loses. The AI is an average for typical conditions, so needs are higher on hot days or after heavy exercise.
The AI isn’t a minimum
Because the AI reflects average intakes of healthy, well-hydrated people, drinking a little less on a given day doesn’t mean someone is dehydrated. The report notes that, for healthy people, thirst and drinking with meals generally keep intake where it needs to be.
Some people need different amounts
People with certain medical conditions, such as kidney or heart conditions, may be told to drink more or less than these averages. Medical advice for your situation comes first. Pregnancy and breastfeeding change needs too; for pregnancy dates, see the due date calculator.
For daily energy needs rather than fluids, use the calorie calculator.
Frequently Asked Questions
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 aged 19 and over. That's total water from all drinks and food. Since roughly 80% usually comes from drinks, that's about 3.0 liters (12.5 cups) of fluids for men and 2.2 liters (9 cups) for women.
Does the water in food count?
Yes. The adequate intakes are for total water, which includes water in food such as fruit, vegetables and soups. The National Academies report notes that about 20% of total water typically comes from food and 80% from drinks.
Do coffee, tea and other drinks count?
The adequate intakes count water from all beverages, not just plain water. The calculator's drinks figure covers everything you drink.
How much water do I need when pregnant or breastfeeding?
The adequate intake of total water is 3.0 liters a day during pregnancy and 3.8 liters a day while breastfeeding, according to the National Academies' reference values. A doctor or midwife can give guidance for your own pregnancy.
Is 8 glasses a day the right amount?
The National Academies didn't set a fixed number of glasses. Their adequate intakes for total water are about 15.6 cups a day for men and 11.4 cups for women, from food and drinks combined.
Do I need more water when exercising or in hot weather?
Water needs vary from day to day with physical activity and climate, and the adequate intakes are averages for healthy people. Thirst and drinking with meals usually cover daily needs for healthy people, according to the report.
Related Calculators
- Calorie CalculatorDaily calories to maintain weight, at four activity levels.
- BMR CalculatorCalories burned at rest, using the Mifflin–St Jeor equation.
- BMI CalculatorBody mass index, CDC weight category and healthy weight range.
- Due Date CalculatorEstimated due date from last period, conception or IVF transfer.
Sources
- National Academies (Institute of Medicine). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC — National Academies Press, 2005.
- Dietary reference values for total water, including pregnancy (3.0 L/day) and lactation (3.8 L/day) — summary table in Nutrients 2018;10(12):1928
- VOA Special English Health Report, March 2, 2004 — coverage of the IOM report; most healthy people meet their daily fluid needs by letting thirst be their guide
- The drinks/food split uses the report's typical 80/20 proportion. Cups are US cups (8 fl oz, 236.6 mL).
Last reviewed: