Daily water intake calculator

How much water should you drink a day?

About 74 ounces (2.2 liters, or 9 cups) a day for women and 101 ounces (3.0 liters, or 13 cups) for men, from all drinks. Those are the U.S. National Academies' figures for an average adult in a mild climate.

The full recommendation is a little higher: about 2.7 liters of total water a day for women and 3.7 for men. That total includes the water in food, which usually supplies about a fifth of it. The numbers above are the share that comes from what you drink.

One number doesn't fit everyone. A larger body needs more, and so does anyone who exercises or lives somewhere hot, cold or high up. That's what the calculator adjusts for.

Water intake by weight: chart in ounces and liters

How much water should you drink if you weigh 150, 200 or 250 pounds? This chart shows the daily amount at common body weights, calculated with the same function as the tool above, before adding anything for exercise or heat.

Fluids a day from all drinks, for someone who is sedentary in mild weather. To turn ounces into 16.9-oz bottles, divide by 17.

How this water intake calculator works

It takes three steps:

1. Start from the National Academies figure for your sex: 74 ounces a day from drinks for women, 101 for men.
2. Raise it for a larger body. If 0.46 ounces per pound of your weight is more than that figure, the calculator uses it, up to about 34 extra ounces.
3. Add for activity and climate: a set amount for each activity level, and more for hot or humid weather, cold or high altitude.

Half your body weight in ounces

You may have heard that you should drink half your body weight in ounces. It's a rule of thumb with no study behind the exact number, but it lands close for most people. At 200 lb it says 100 ounces, and the calculator gives a 200 lb woman 92 ounces, or 109 if she's moderately active. Where the rule goes wrong is at higher weights, because it has no upper limit.

8 glasses of water a day

Eight 8-ounce glasses is 64 ounces. There's no research behind that specific number either. It's a little under the National Academies figure for women and well under the one for men.

What raises your water needs: exercise, heat, cold and altitude

You lose water through sweat, so the more you move and the hotter it is, the more you need to replace. The calculator adds a set amount for each activity level:

The climate counts too. The calculator adds 17 ounces for hot or humid weather, 8 ounces for cold weather, when dry air takes more water out with every breath, and 25 ounces at high altitude, where you breathe faster and lose more that way. These are sensible starting points, not exact measurements: how much you sweat varies a lot from person to person. On a long or hard workout, drink before, during and after.

How much water should you drink on a GLP-1?

The same amount as anyone your size. No guideline sets a higher number for people on semaglutide or tirzepatide, so this calculator doesn't add anything for them. What the medication changes is how easy the target is to reach:

• You eat less, and food normally supplies about a fifth of your water.
• Some people feel less thirsty, along with less hungry.
• Nausea, vomiting or diarrhea can make fluids harder to keep down. The prescribing information for the brand-name medications warns that fluid loss from vomiting or diarrhea can lead to kidney problems.

A few habits help:

• Keep a water bottle with you and sip through the day, not all at once.
• Drink between meals if a full stomach bothers you.
• Check the color of your urine: pale yellow is a good sign, and dark yellow usually means you need more fluids.

Contact your care team if you can't keep fluids down, feel dizzy, or are urinating much less than usual.

Thirst, dehydration and electrolytes on semaglutide or tirzepatide

Thirst can go either way on a GLP-1: some people notice less of it, and others feel thirstier. For why, and what to drink, see our guide to hydration on GLP-1s. Since thirst can change on treatment, watch for the other signs of dehydration: dark urine, a dry mouth, headache, dizziness and feeling unusually tired.

Do you need electrolytes?

Most days, no. If you're eating and drinking normally, plain water and other everyday drinks are enough: most people get plenty of sodium from food, and fruit, vegetables, beans, dairy and potatoes supply potassium. Electrolytes matter when you lose fluids quickly. Vomiting and diarrhea drain sodium and potassium along with water, and so does heavy sweating.

On those days, sip fluids steadily, and a sugar-free or low-sugar oral rehydration drink can help replace what you've lost. Read more about electrolytes on GLP-1s and how to manage GLP-1 side effects.

Get medical care right away for severe or persistent vomiting, severe abdominal pain, or signs of serious dehydration such as confusion, fainting or very little urine.

Does drinking water help you lose weight?

It helps a little, and mostly indirectly. Water doesn't burn fat or make a medication work better. What it can do:

• Replace calories. Water has none, so drinking it in place of soda, juice or sweetened coffee lowers what you take in.
• Take the edge off a meal. In one 12-week study of middle-aged and older adults on a reduced-calorie diet, those who drank about two cups of water before each meal lost somewhat more weight. It's one small study, so treat it as a habit worth trying, not a guarantee.
• Help with constipation, which is common when you eat less.

Weight loss still comes from eating fewer calories than you burn. The calorie deficit calculator shows how many, and the protein calculator shows how much protein to eat along the way.

What counts toward your water intake?

All drinks count, not only plain water:

• Water and sparkling water. Both count fully.
• Coffee and tea. They count. Caffeinated drinks still add more fluid than they cost you. Wondering about caffeine on treatment? See coffee on semaglutide.
• Milk, broth and soup. They count too.
• Food. Fruit, vegetables and other watery foods supply about a fifth of most people's water. The calculator's number is for drinks, so food is already accounted for.

Plain water is the easy default, because it has no calories or sugar.

Can you drink too much water?

Yes, though it's rare. The risk is speed, not the daily total: healthy kidneys can clear roughly 0.7 to 1 liter an hour, and drinking far more than that in a short time can dilute the sodium in your blood.

The fix is simple. Spread your water through the day instead of drinking it all at once. The calculator's highest possible result is 5.8 liters (194 ounces), for a very large man who is extra active at high altitude. If your clinician has told you to limit fluids, follow that number instead.