How much water should I drink a day?
Updated October 13, 2026 by madebykamal
The US National Academies set an adequate intake of about 125 fl oz (3.7 liters) of total water a day for men 19 and older and 91 fl oz (2.7 liters) for women, food included, with about 101 fl oz (13 cups) and 74 fl oz (9 cups) of it from drinks. Pregnancy and breastfeeding raise the drinks part to about 78 and 105 fl oz, and exercise and heat add more, depending on how much you sweat. Enter your age and sex below for your figure, with an optional workout sweat check and time in the heat.
General information, not medical advice. How these guides are made.
Where each figure comes from
| Figure | Source |
|---|---|
| Adequate intakes of total water and of drinks by age, sex, pregnancy and breastfeeding; drinks about 81% and food about 19% of total water for adults 19 to 30; higher needs with activity and heat | National Academies: Dietary Reference Intakes for Water, chapter 4 |
| No specific recommendation for how much plain water to drink; needs depend on sex, weight, age, activity and medical conditions | MedlinePlus: Water in diet |
| Sweat loss equation; adult sweat rates of 0.5 to 4.0 L an hour; a loss under 2% of body weight; no weight gain during exercise; 100 to 150% replacement afterward; drinking to thirst when the sweat rate is unknown | NATA position statement: Fluid Replacement for the Physically Active (2017) |
| 1 cup (8 fl oz) every 15 to 20 minutes for moderate activity in the heat lasting less than 2 hours; generally no more than 6 cups an hour; sports drinks when sweating lasts several hours | CDC NIOSH: Heat stress, workplace recommendations |
| No upper limit for healthy people; water toxicity from drinking faster than the kidneys' maximum of about 0.7 to 1.0 L an hour | National Academies, chapter 4 |
| Heart failure, kidney disease and advanced liver disease among the causes of low blood sodium; its symptoms | MedlinePlus: Low blood sodium |
| 1 lb = 0.45359237 kg; 1 US fl oz = 29.5735 ml; 1 cup = 8 fl oz | NIST SP 811, Appendix B.8 |
Checked on . Results are rounded: fluid ounces and daily cups to the nearest whole, liters to one decimal (two below 1 L), weights and percentages to one decimal. Nothing you enter leaves this page.
Daily water by age, sex, pregnancy and breastfeeding
These are the adequate intakes (AIs) in the National Academies' Dietary Reference Intakes for water: total water from drinks and food, set from median intakes in a US national survey, with the drinks part beside it:
- Men 19 and older: 125 fl oz (3.7 L) in total, about 101 fl oz (13 cups, 3.0 L) from drinks.
- Women 19 and older: 91 fl oz (2.7 L) in total, about 74 fl oz (9 cups, 2.2 L) from drinks.
- Pregnancy, ages 14 to 50: 101 fl oz (3.0 L) in total, about 78 fl oz (10 cups, 2.3 L) from drinks.
- Breastfeeding, ages 14 to 50: 128 fl oz (3.8 L) in total, about 105 fl oz (13 cups, 3.1 L) from drinks.
- Ages 14 to 18: boys 112 fl oz (3.3 L) in total, about 88 fl oz (11 cups) from drinks; girls 78 fl oz (2.3 L), about 61 fl oz (8 cups) from drinks.
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On a computer? Scan this with your iPhone camera to open it in the App Store.What the figure means
It does not change after 19. In the survey data for adults aged 19 to 30, drinks supplied about 81 percent of total water and food about 19 percent, and the academies found that caffeinated drinks appear to count much as other drinks do. They also say a wide range of intakes is compatible with normal hydration, so the AI is not a specific requirement: day to day, thirst and drinks with meals keep healthy people hydrated. For children under 14, see the guide How Much Water Should a Child Drink a Day?
Why the calculator does not ask for your weight
The National Academies set the AI by age, sex and life stage and give no amount per pound or per kilogram for adults, so the calculator does not use weight or height for the daily figure. MedlinePlus (National Library of Medicine) says individual needs depend on sex, weight, age, activity and medical conditions, but also that there is no specific recommendation for how much water to drink. Weight counts in the workout check, where the scale measures what you sweated.
Exercise: measure your own sweat loss
The National Athletic Trainers' Association (NATA) says adult sweat rates during exercise range from 0.5 to 4.0 L (17 to 135 fl oz) an hour, and that fluid advice should rest on individual data, not population estimates, so the calculator adds no fixed amount per hour. Its workout check uses NATA's method:
- Sweat loss is your weight before minus your weight after, plus what you drank, minus any urine passed. A kilogram counts as a liter, a pound as about 15 fl oz; divide by the hours for your sweat rate.
- End with a loss of less than 2 percent of body weight, and not heavier than you started: drinking beyond sweat losses can cause exercise-associated hyponatremia.
- Afterward, replace 100 to 150 percent of the loss, up to 150 percent when recovery time is under 4 hours.
Hot weather and work in the heat
The National Academies say hot environments raise water needs but set no added amount, so the calculator adds nothing for heat alone. For moderate work or activity in the heat lasting less than 2 hours, NIOSH, part of the CDC, advises 1 cup (8 fl oz) of water every 15 to 20 minutes, or 24 to 32 fl oz an hour, and the calculator adds that for the minutes you enter. NIOSH says intake should generally not exceed 6 cups (48 fl oz) an hour, with sports drinks containing electrolytes when sweating lasts several hours.
When more water is a risk
The National Academies set no upper limit for water in healthy people, but note that water toxicity has been reported after people drank large amounts faster than the kidneys' maximum of about 0.7 to 1.0 L (24 to 34 fl oz) an hour, and that the resulting low blood sodium (hyponatremia) can be life threatening.
MedlinePlus lists heart failure, kidney disease and advanced liver disease among its causes, and limiting water among its treatments. With one of these conditions, or a fluid limit from your clinician, follow that limit, not this calculator. MedlinePlus says to call your provider right away if symptoms appear: confusion, irritability, headache, fatigue, nausea or vomiting, muscle weakness or cramps, or convulsions.
Keeping track with HydroNest
HydroNest Family Water Tracker gives each person in a household a profile with a daily goal calculated from age, weight and activity, on one phone; family profiles are part of HydroNest Premium. It counts 38 drinks, from water and coffee to juice, with hydration factors drawn from published research on the Beverage Hydration Index, and logs from widgets, an Apple Watch app or Siri. Data stays on your device and in your own iCloud, with no account. HydroNest is a hydration log, not a medical device; if a condition affects how much you should drink, follow your doctor.
Questions people ask
How much water should I drink a day in oz?
From drinks, water included, the National Academies' figures are about 101 fl oz (13 cups) a day for men 19 and older and 74 fl oz (9 cups) for women, or 78 fl oz in pregnancy and 105 fl oz while breastfeeding. With food, the totals are 125 fl oz for men and 91 fl oz for women.
How much water should I drink a day while pregnant?
In pregnancy the National Academies set 101 fl oz (3.0 L) of total water a day, about 78 fl oz (10 cups) from drinks, for ages 14 to 50. Breastfeeding raises it to 128 fl oz (3.8 L), about 105 fl oz (13 cups) from drinks.
Is there a water intake calculator by weight?
The main US reference, the National Academies' adequate intake, is set by age and sex, not weight or height. Weight matters for exercise: weighing yourself before and after a workout, as NATA describes, shows how much you sweated, and this calculator adds that to your daily figure.
Related
- How Much Water Should a Child Drink a Day? By Age
- How Much Water Should a Dog Drink a Day? By Weight
- How Much Water Should a Cat Drink a Day? By Weight
- Dog and Cat Water Intake Calculator, by Weight
- HydroNest Family Water Tracker
Sources
- https://www.nationalacademies.org/read/10925/chapter/6
- https://medlineplus.gov/ency/article/002471.htm
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5634236/
- https://www.cdc.gov/niosh/heat-stress/recommendations/index.html
- https://medlineplus.gov/ency/article/000394.htm
- https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8