How many ounces of water should I drink a day?

Most healthy adults need about 64 to 100 ounces of fluid from drinks. A simple rule is half an ounce per pound of body weight. The U.S. National Academies' estimates work out to roughly 99 ounces from drinks for men and 74 for women.

Is 64 ounces of water a day enough?

For many people, yes. It's the “8 by 8” goal, and it's a reasonable place to start. Smaller or less active adults may do well on it, while larger or more active people usually need more. Pale yellow urine is a good check.

How many ounces of water should a 150-pound person drink?

About 75 ounces a day by the half-ounce rule, which is roughly 2.2 liters. Add more on days you exercise or when it's hot.

Is 100 ounces of water a day too much?

Not for most healthy adults. It's close to what the National Academies estimate men get from drinks, and a 200-pound person lands there by the body-weight rule. Spread it through the day, and follow your doctor's advice if you have a kidney or heart condition.

How many 16.9-ounce water bottles is that?

64 ounces is about four bottles, 80 ounces is about five, and 100 ounces is about six.

Does the water in food count toward my ounces?

Yes. Food supplies about 20 percent of your total water, which is why the drinks-only goals are lower than the total figures.

How many ounces of water should I drink to lose weight?

There's no special number. Water has no calories, so choosing it over sugary drinks can lower the calories you take in. Use the chart for your daily goal and keep it steady.

How Many Ounces of Water Should You Drink a Day?

Most healthy adults need roughly 64 to 100 ounces of fluid from drinks each day. Your own number depends mostly on your body size, how active you are, and how hot it is where you live.

Below you'll find the official numbers in ounces, a simple chart by body weight, and a practical way to hit your goal without doing math in your head.

Quick answer: drink about half an ounce of water for every pound you weigh. A 160-pound person aims for around 80 ounces a day. Exercise, heat, pregnancy and illness push the number up.

What do the official guidelines say, in ounces?

The most cited numbers come from the U.S. National Academies of Sciences, Engineering, and Medicine (Dietary Reference Intakes for Water). They set an adequate total fluid intake, counting water from drinks and food together, at about 15.5 cups (3.7 liters) a day for men and 11.5 cups (2.7 liters) for women. The Mayo Clinic summarizes these figures too.

With 8 fluid ounces in a cup, that works out to:

Men: about 124 ounces of total water a day, which is roughly 99 ounces from drinks.
Women: about 92 ounces of total water a day, which is roughly 74 ounces from drinks.
The “8 by 8” rule: eight 8-ounce glasses, or 64 ounces. It's easy to remember and a reasonable starting goal, but it isn't a scientific limit.

About 20 percent of the water you take in comes from food, which is why the drinks-only figures are lower than the totals. These are averages for healthy adults, not prescriptions.

How many ounces of water should you drink by body weight?

Body size is the biggest thing that changes your number. A simple, widely used rule of thumb is to drink about half an ounce of water for every pound you weigh. That's the same as about 33 milliliters per kilogram.

Here is what that looks like at common body weights:

100 lb (45 kg): about 50 oz (1.5 L)
120 lb (54 kg): about 60 oz (1.8 L)
140 lb (64 kg): about 70 oz (2.1 L)
160 lb (73 kg): about 80 oz (2.4 L)
180 lb (82 kg): about 90 oz (2.7 L)
200 lb (91 kg): about 100 oz (3.0 L)
220 lb (100 kg): about 110 oz (3.3 L)

Treat the chart as a starting point, not a rule. Add to it if you exercise, live somewhere hot, or are pregnant or breastfeeding, and ask your doctor if you have a kidney or heart condition or take a medicine that affects fluids. If you think in liters, our guide to how much water you should drink a day covers the same ground.

What changes how many ounces you need?

Your chart number is the baseline. These things move it up:

Exercise. Sweat is lost water, so you need more on workout days.
Hot or humid weather. You sweat more even when you're sitting still.
High altitude. You lose more fluid through faster breathing and more urination.
Illness. Fever, vomiting and diarrhea all drain fluid quickly.
Pregnancy and breastfeeding. Both raise your needs. Your doctor can give you a number that fits you.

How much water should you drink when you exercise?

The American Council on Exercise gives a simple schedule for a workout (ACE Fit Facts on hydration):

2 to 3 hours before: about 17 to 20 ounces.
20 to 30 minutes before: about 8 ounces.
During: about 7 to 10 ounces every 10 to 20 minutes.
Within 30 minutes after: about 8 ounces.

That's general guidance for moderate exercise. Long or very hot sessions call for more.

Do coffee, tea and other drinks count?

Yes. Tea, coffee, milk, juice and sparkling water all count toward your fluid total. Water is the best default because it has no calories, sugar or caffeine, but you don't have to count only plain water.

Water-rich foods such as soup, fruit and vegetables count too. They supply about a fifth of what you take in, so you don't need to make up for them with extra glasses.

How do you know if you're drinking enough?

Your body gives you easy clues:

Pale yellow urine is the sign you're about right. Dark yellow or amber means drink more.
Rarely thirsty and passing urine every few hours is a good sign.
Dry mouth, headache, tiredness or dizziness can mean you've fallen behind.

Can you drink too much? It's uncommon, but it's possible. Drinking very large amounts very quickly can dilute the sodium in your blood. Spread your water through the day, and don't force it.

How to actually hit your number

Do the bottle math. A standard 16.9-ounce (500 ml) bottle is about two 8-ounce glasses. If your goal is 80 ounces, that's about five bottles.
Tie sips to things you already do. A glass when you wake up, one with each meal, and one at your desk covers most of a day.
Drink more earlier. Front-loading your water helps if night-time bathroom trips bother you.
Keep a bottle in sight. If you can see it, you'll drink it.
Track it. A running total turns “I think I drank enough” into a number.

If remembering is your real problem, read how to remember to drink water during a busy workday.

Track your ounces without the math

Hydrabit turns your number into a simple daily goal. Set it in fluid ounces or milliliters, log each glass with a tap, and watch the day fill up.

Your goal in ounces: adjustable any time, with an optional suggestion based on your weight, activity and climate.
One-tap logging: pick an amount, tap Add, and you're done. You can log from your Apple Watch too.
Reminders that stop once you've hit your goal.
Streaks and Apple Health: see the days you met your goal, with your water saved to Health.
Free to use, with no account to create.

Download Hydrabit on the App Store and set your daily ounces in under a minute.

Frequently Asked Questions

The bottom line

Start with half an ounce of water per pound of body weight, adjust for exercise, heat and your health, and aim for pale yellow urine. The number matters less than a habit you can keep.

Pick your ounces, log your glasses, and let reminders do the remembering. Download Hydrabit to set your daily goal in ounces.