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Water Calculator: How Much Water to Drink Daily

By Dawn Colclasure Last Updated September 22, 2022 Medically Reviewed by Leilani Fraley, RN, MSN
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Photo Courtesy: fizkes | iStock by Getty Images

Knowing how much water to drink daily can help your body function like the well-lubricated engine it is. But knowing how much water to drink a day, in general, is just the start. Read on to find out how to calculate your fluid needs, why drinking water is so good for your health and which water-rich foods help boost hydration.

What Are the Benefits of Drinking Water?

Water makes up about 50% to 70% of your body weight. But you lose a lot of water when you breathe, sweat, urinate and have bowel movements.

Knowing how much water to drink daily helps replenish your water stores more effectively. In turn, this can help your body:

  • Control blood pressure and heart rate
  • Deliver nutrients and oxygen-rich blood to cells, tissues and organs
  • Digest foods
  • Filter and remove waste and toxins
  • Get your bowels moving easily, especially if you’re constipated
  • Prevent kidney damage and disease
  • Protect, lubricate and cushion joints, bones, skin, brain and spinal cord
  • Regulate body temperature

Water may also help you perform better when you exercise, support weight loss and ease your allergy and asthma symptoms.

What Happens When You Don’t Drink Enough Water?

Thirst isn’t the best way to tell how much water to drink per day. Nor is it the most dependable indicator of dehydration — a health condition that occurs when your body doesn’t have the water it needs to function well. 

In fact, you may already be dehydrated by the time you feel thirsty. Along with thirst, dehydration can make you feel:

  • Confused
  • Dizzy, faint or lightheaded
  • Tired
  • Very hot or cold

You may also have:

  • Cravings for sugar but little to no appetite
  • Dark urine
  • Dry cough, mouth or tongue
  • Flushed or dry skin
  • Headache
  • Muscle cramps
  • Rapid pulse but low blood pressure

Severe dehydration can also shrink the blood vessels in your brain. This can affect brain functions such as thinking, memory, reaction time, balance and coordination.

You’ll also urinate less since your kidneys hold onto urine when the fluid volume in your blood gets too low. This means your kidneys are getting rid of less waste and toxins from your body.

Is 64 Oz of Water a Day Enough?

In the 1940s, the U.S. Food and Nutrition Board (USFNB) advised the public on how much water to drink a day. Their advice: Drink 10.5 cups (84.5 ounces) per day. 

The problem is the USFNB never actually cited clinical research to support these guidelines. Over the years, this became the “8 cups (64 ounces) of water daily” rule we now know. 

What Happens If You Drink Too Much Water?

Can you drink too much water? You can overhydrate your body when you chug more water than your body needs. 

But this doesn’t happen all that easily or to most people, especially if your kidneys, heart, liver and pituitary gland work normally. A healthy young adult would need to drink around 6 gallons or more of water per day on a routine basis.

Overhydration can throw off your body’s electrolyte balance. These include vital minerals such as sodium, potassium, magnesium and chloride. When you overhydrate, the amount of sodium in your blood gets diluted.

And when sodium levels drop too low, hyponatremia can develop. This is a serious health condition that can cause headaches, nausea and vomiting. You may also have muscle spasms, cramps and weakness. 

If your hyponatremia becomes severe, you may show signs of water toxicity (also called water poisoning or water intoxication). You may appear confused and disoriented and have hallucinations and delusions. Without prompt treatment, these symptoms can progress to delirium, seizures, coma and even death.

How Much Water Do I Need to Drink a Day?

The National Academy of Medicine (NAM) provides general recommendations on how much water to drink daily for most healthy adults living in temperate climates:

  • 15.5 cups (124 fluid ounces) for males
  • 11.5 cups (92 fluid ounces) for females

NAM recommends these daily fluid recommendations for kids and teens:

  • 1 to 3 years-old  = 4 cups (32 ounces)
  • 4 to 8 years-old  = 5 cups (40 ounces)
  • 9 to 13 years-old = 7 to 8 cup (56 to 64 ounces)
  • 14 to 18 years-old = 8 to 11 cups (64 to 88 ounces) 

Pregnant and breastfeeding mothers may need upwards of 13 to 16 cups of healthy fluids daily. 

Can My Fluid Needs Change?

Along with your age and birth gender, your lifestyle, activity level and health status can also influence how much water to drink each day. For instance, these can increase your fluid needs:

  • Drinking alcohol
  • Exercise, especially lengthy and intense workouts
  • Fever
  • Prolonged vomiting and diarrhea
  • Extreme temperatures (very hot or cold)
  • High altitudes 

You may also need to take in more fluids if you’re an older adult. That’s because your body’s fluid volume goes down with age. Also, you may not regulate your body temperature as well as you did when you were younger. 

You may take medicines and have 1 or more chronic health conditions that raise your risk for dehydration. These include diabetes, heart disease, high blood pressure and obesity. All of these also make you more prone to heat illness.

How to Calculate How Much Water to Drink

A simple water calculator formula sums up how much water to drink daily. Drink half your body weight in ounces of water:

Your weight x 0.5 = daily fluid needs

Example: 200 pounds x 0.5 = 100 fluid ounces

Water Calculator for Pregnant and Breastfeeding Mothers

If you’re pregnant or breastfeeding, drink your usual amount of daily fluids plus 24 to 32 ounces more.

Daily fluid needs + 24 to 32 = daily fluid needs for pregnant and breastfeeding mothers

Example: 100 + 24 to 32 = 124 to 132 fluid ounces 

Water Calculator With Workouts

On top of your usual daily fluid needs, add 12 ounces of water for every 30 minutes of exercise:

Daily fluid needs + (exercise minutes ÷ 30 ✕ 12) = daily fluid needs with exercise

Example: 100 + (60 ÷ 30 ✕ 12) = 124 fluid ounces

How to Stay Hydrated With Other Fluids

Water from the tap or store isn’t the only way to meet your daily fluid needs. You can hydrate with whole (100%) fruit juices, teas and dairy and plant-based milks. Watch the added sugars and preservatives in store-bought products, though, if you’re concerned about other health issues. 

And if coffee is your drink of choice, you can have around 2 cups of your favorite brew without worrying about dehydration. That’s around 180 milligrams of energy-boosting caffeine.

If you’re feeling a bit more adventurous, try:

Foods With High Water Content

How much water to drink daily isn’t the only question to answer. Also, consider how to meet your fluid needs with water-rich foods such as fruits and vegetables. 

NAM recommends that 20% of your daily fluids come from these foods. Melons, cucumbers, berries, pineapples, kiwi and portobello mushrooms are among the many flavorful and water-dense foods you can add to your hydration repertory. 

Does Sparkling Water Hydrate You?

Sparkling water can hydrate your body just as well as plain water. They’re a far healthier choice than drinks with added sugars and artificial sweeteners such as regular or diet soda. These fizzy drinks can for sure help you with your daily fluid needs, especially if drinking plain water doesn’t suit your taste buds.

Does Alcohol Dehydrate You?

Alcohol is a diuretic. It keeps your pituitary gland from releasing antidiuretic hormone (also called vasopressin), a hormone that helps your kidneys work properly. As a result, your kidneys flush out more liquid than usual.

This can cause dehydration, especially if you drink alcohol on an empty stomach. If you choose to have alcohol, be sure to have water-rich foods with your drink. Also, sip water with your alcoholic drink, have a cup of water in between servings or add water to it.

How Can I Tell If I’m Getting Enough Fluids?

Your body usually tells you how much water to drink daily. But don’t rely on thirst alone. Let your poop do the talking. If you’re often constipated, you likely need to up your fluid game. 

Also, peek at your pee and take the whiff test. If it’s dark and has a strong odor, you likely need to get more fluids in you. But if your urine’s odorless and pale yellow, you’re right on target. 

Lastly, feel your skin out. Dehydrated skin looks dull and feels itchy and tight. You’ll also notice more fine lines and wrinkles and deeper, darker undereye circles.

Gently pinch your arm, abdomen, cheek or finger knuckle for 3 seconds. For most people, dehydration causes the skin to stay tented (i.e., pinched) longer than normal.

On the other hand, well-hydrated skin retains water. Thus, it’ll snap back in place quickly. This is known as skin turgor or elasticity, referring to its ability to change shape and then quickly return to normal.

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