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

But calculating the amount of water you need daily is more complicated than you might think. “The idea that everyone needs eight 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?

• About 3.7 liters per day for men (about 16 cups)
• About 2.7 liters per day for women (about 12 cups)

These totals include water consumed in other beverages, such as:

• Tea
• Coffee
• Sparkling water
• Kombucha
• Coconut water

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.

Age

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

“Dehydration can exacerbate or make other health conditions worse,” says Kalisha Bonds Johnson, PhD, 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 Sex

“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.”

Pregnancy and Nursing

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

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 dehydrate you.

Don’t Flood Your System All at Once

“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.”

• 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.