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Hydration Calculator: How Much Water Do You Need to Drink in a Day?

Hydration Calculator: How Much Water Do You Need to Drink in a Day?
Everyday Health
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Updated on June 6, 2025
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Staying well hydrated has positive effects on virtually every system in your body. It keeps your heart pumping and your joints well lubricated, and regulates body temperature. Drinking enough water can stave off problems like kidney stones and constipation. Adequate hydration may also improve cognition and your mood.

But calculating the amount of water you need daily is more complicated than you might think. “The idea that everyone needs 8 cups of water a day is a helpful starting point, but hydration is not one-size-fits-all because everyone’s body, lifestyle, and health goals are different,” says Grace Derocha, RD, CDCES, a spokesperson for the Academy of Nutrition and Dietetics.

Here’s what to know about how various factors affect the amount of water you need.

How Much Water Should I Drink?

These are the general recommendations for adults:

  • About 3.7 liters per day for men (about 16 cups)
  • About 2.7 liters per day for women (about 11 cups)

These totals include water consumed in other beverages:

To give yourself a better sense of how much water you need to drink each day, use this hydration calculator.



Factors That Affect Fluid Needs

The general recommendations for water intake are a good starting point, but your individual needs can vary based on other factors, such as age and activity level. Here are some of the factors that influence how much water you need.

Activity Level

When you sweat during exercise or on a hot summer day, you need to replace the fluids you’ve lost by drinking more water.

The intensity and duration of exercise affect how much you sweat and your subsequent fluid needs. The temperature also affects how much you sweat, as does your body weight and composition. You don’t have to visibly sweat to become dehydrated, which can happen while swimming in a pool or lake, or skiing on a winter day.

Calculating exact hydration losses from physical activity is complicated because people sweat at different rates. People of the same gender and weight, and with similar diets, will sweat different amounts in the exact same conditions, thus need different amounts of fluid.

Age

Children and teens need proportionally more water than adults relative to their body size, especially during growth spurts and active play, says Derocha.

Older adults may experience a reduced sense of thirst and may need to be more mindful about drinking regularly, even if they don’t feel thirsty. Research has found that chronic dehydration is a common problem in adults. In older adults, the chronic dehydration rate in the United States ranges from 17 to 28 percent.

“Dehydration can exacerbate or make other health conditions worse,” says Kalisha Bonds Johnson, PhD, RN, an assistant professor at Emory University’s Nell Hodgson Woodruff School of Nursing in Atlanta. “Dehydration or inadequate hydration can lead to confusion, poor blood pressure regulation, and poor kidney health. The effects of dehydration on the kidneys can result in a urinary tract infection, which can lead to delirium and also exacerbate symptoms of dementia until corrected.”

Body Weight and Birth Sex

Hydration needs are influenced by the surface area of the body, metabolic rate, and body weight.

“Muscle tissue is about 75 percent water, while fat tissue is only about 10 percent water,” says Derocha. “As a result, as body weight increases, fluid needs increase.”

Compared with people born female, those born male generally need more fluid to support their increased body mass, lower average body fat, and increased calorie burn each day. Men typically sweat more than women.

Pregnancy and Nursing

Pregnant women require additional fluids to maintain amniotic fluid levels, increase blood volume, and keep the baby growing steadily.

If you're nursing a growing baby, you need to drink more fluids so that your body can make enough milk.

 Derocha says that a nursing mother typically needs about 16 cups (3.8 liters) per day total — with about 3 cups of that specifically to support milk production.

Diet Quality

The foods you eat affect your hydration and the amount of fluid you need to drink. If you eat ample fruits and veggies each day, you don’t need to drink as much water. Some fruits and vegetables have higher water content than others. Watermelon and spinach, for example, are especially hydrating, as they are almost 100 percent water by weight. Soup is another fluid-rich food that can help you meet your target water intake.

If your fruit and vegetable intake is low on a given day, a few extra glasses of water will compensate. Drinking extra water when drinking alcohol is also a good idea, as alcohol is a diuretic and can make you dehydrated.

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Don’t Flood Your System All at Once

Drinking water gradually throughout the day is important. However, drinking excessive amounts of water at once may increase the risk of an extremely rare condition called hyponatremia, or water intoxication, which occurs when the electrolytes in the body become depleted. This is more likely to affect endurance athletes or people with kidney disease.

“Sodium is essential for maintaining normal fluid balance, nerve function, and muscle activity,” says Derocha. “When there’s too much water and not enough sodium, water starts to move into cells, causing them to swell.”

Symptoms of hyponatremia may include the following:

  • Nausea and vomiting
  • Headache
  • Confusion or disorientation
  • Muscle cramps or weakness
  • Fatigue
  • Seizures, coma, or even death in severe cases

Derocha says that, in general, people should listen to their bodies to help guide how much water they need. “Instead of rigid rules, I encourage people to listen to their body’s cues. Thirst, urine color — aim for light yellow — energy levels, and even mood can all be helpful indicators of hydration status,” she says.

The Takeaway

  • Staying well hydrated is critical for keeping your body healthy and can also have positive effects on cognition and mood.
  • While there are general guidelines for how much water people should drink, hydration needs can vary widely depending on your sex, weight, and fitness habits.
  • Water intake can also be increased by eating foods with a high water content.
  • Though it’s very rare, it is possible to consume too much water, which can be dangerous.
  • In general, listen to your body when figuring out how much water to drink. Be aware of how your age or other conditions might affect your water intake needs.

Whatever your water intake goal, a water bottle will help you get there. We tested a wide variety of options — and picked our 12 favorites.

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. 10 Reasons Why Hydration is Important. National Council on Aging. January 2, 2025.
  2. Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk. National Academies of Sciences, Engineering, Medicine. February 11, 2004.
  3. Hydrate Right. Academy of Nutrition and Dietetics. May 19, 2023.
  4. Taylor K et al. Adult Dehydration. StatPearls. March 5, 2025.
  5. Water – A Vital Nutrient. Better Health Channel. May 12, 2023.
  6. Rosinger AY et al. Variation in Urine Osmolality Throughout Pregnancy: A Longitudinal, Randomized-Control Trial Among Women with Overweight and Obesity. European Journal of Nutrition. July 3, 2021.
  7. Nursing Your Baby — What You Eat and Drink Matters. Academy of Nutrition and Dietetics. July 25, 2023.
  8. Water: How Much Should You Drink Everyday? Mayo Clinic. October 12, 2022.
  9. Water Intoxification. Cleveland Clinic. September 17, 2024.
  10. Hyponatremia. Mayo Clinic. May 17, 2022.
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Reyna Franco, RDN

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Reyna Franco, RDN, is a New York City–based dietitian-nutritionist, certified specialist in sports dietetics, and certified personal trainer. She is a diplomate of the American College of Lifestyle Medicine and has a master's degree in nutrition and exercise physiology from Columbia University.

In her private practice, she provides medical nutrition therapy for weight management, sports nutrition, diabetes, cardiac disease, renal disease, gastrointestinal disorders, cancer, food allergies, eating disorders, and childhood nutrition. To serve her diverse patients, she demonstrates cultural sensitivity and knowledge of customary food practices. She applies the tenets of lifestyle medicine to reduce the risk of chronic disease and improve health outcomes for her patients.

Franco is also a corporate wellness consultant who conducts wellness counseling and seminars for organizations of every size. She taught sports nutrition to medical students at the Albert Einstein College of Medicine, taught life cycle nutrition and nutrition counseling to undergraduate students at LaGuardia Community College, and precepts nutrition students and interns. She created the sports nutrition rotation for the New York Distance Dietetic Internship program.

She is the chair of the American College of Lifestyle Medicine's Registered Dietitian-Nutritionist Member Interest Group. She is also the treasurer and secretary of the New York State Academy of Nutrition and Dietetics, having previously served in many other leadership roles for the organization, including as past president, awards committee chair, and grant committee chair, among others. She is active in the local Greater New York Dietetic Association and Long Island Academy of Nutrition and Dietetics, too.

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Kelly Kennedy is a licensed dietitian-nutritionist with over 14 years of experience in digital media. She previously managed and oversaw nutrition content, recipe development, meal planning, and diet and nutrition coaching at Everyday Health. She developed and reviewed various meal plans, books, slideshows, and online tools, and oversaw the creation of more than 500 unique recipes. She received her bachelor's degree from the University of Massachusetts, Amherst, and a master's degree from the State University of New York College at Oneonta.

Kennedy enjoys anything that takes her outside, from gardening and playing in the yard with her kids to hiking and even feeding her pet chickens.

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